endocrine system

• endocrine system focuses on chemical potential and reactions to signals
• endocrine glands lack ducts, exocrine have ducts
• endocrine coordinates responses to:
  • environmental challenges (stress)
  • growth, development, reproduction (growth hormone)
    • ecdysteroid/juvenile hormones
  • homeostasis
• hormones stored in endocrine glands and transported almost directly into blood → remote targets
  • act on far targets in the body
  • low concentrations of hormones have disproportionately large effects on their cells: amplification
  • main classes of hormones: steroid and non-steroid
• steroid hormones: lipid-based, fatty structures
  • permeate target cell membranes and bind to internal receptors
  • lock-and-key hormones
  • steroid hormone passes through all cells but only affects target
  • affects gene expression (transcription/translation)
    • repeat transcription and translation amplifies signal
• non-steroid hormones: amino acid based, proteinaceous structures
  • epinephrine (adrenaline)
  • bind to receptors on the cell membrane, not internal
  • signal transduction cascade: series of activation of proteins that creates work/activation in existing proteins
    • transmission of message is amplified through the transduction cascade
    • exponential transmission
    • know beginning steps: receptor → g-protein → cyclase → cxmp
    • know ending: activates kinase → enzyme → produces molecules from extant molecules
• case studies
• endocrine system: hypothalamus, pituitary gland, pineal gland, thyroid gland, parathyroid gland, adrenal gland, pancreas, reproductive glands

hypothalamus and the pituitary glands

• pituitary gland is composed of two regions and sits directly underneath hypothalamus
• pituitary develops as two different structures and named regionally; different levels of communication with hypothalamus
• posterior pituitary is a posterior extension of the hypothalamus; hypothalamus connection to posterior pituitary acts as a single structure
• anterior pituitary forms as a separate structure; “pinched” off from organs
• hypothalamus-posterior possesses axons and neurosecretory cells
  • neurosecretory cells act identically to neurons, with axons and synaptic terminals, but the resulting chemicals act like hormones, not neurotransmitters: these are neurohormones
    • neurohormones leave the terminal neurosecretory cells and enter the bloodstream
    • neurohormones act on remote targets
  • posterior-hypothalamus only produces two hormones: oxytocin and antidiuretic hormones (ADH)
    • oxytocin: the aitsf hormone
      • targets the mammary glands: facilitates ejection of milk; facilitates contraction
        • positive feedback
      • targets smooth muscle in uterus: facilitates contraction during child labor
      • targets oxytocin receptors in brain: interpersonal behaviors; “cuddle hormone”
        • high production of oxytocin in parents and newborn
        • oxytocin high during intimacy
        • possible connection to ppd and autism; active research
    • antidiuretic hormones; adh, vasopressin
      • targets the kidney nephrons: modifies excretory filtrate to reclaim water and solutes while leaving nitrogenous waste, etc.; primarily reclaims water through reabsorption
        • during dehydration, adh is secreted and binded to receptors in the nephron to promote reabsorption and maintain homeostasis
        • dehydrated urine is more concentrated: yellow color
        • alcohol inhibits adh, causing urine to dilute and urination to increase; headaches/hangovers result from dehydration
• hypothalamus needs to secrete a separate hormone to communicate with the anterior pituitary gland
  • neurosecretory cells in the hypothalamus are carried to the anterior pituitary gland through portal vessels: connects the capillary bed of the hypothalamus to the c.b. of the anterior pituitary gland
    • unusual, unique setup in the body; imitates a duct without having a physical actual duct between ht and apg
  • hypothalamic tropic hormones are transported with the neurosecretory cells
    • tropic hormone: targets another endocrine gland (vs. effectors); causes the release or inhibition of hormones
    • hypothalamic releasing hormones stimulate endocrine cells in anterior pituitary gland to synthesize hormone vs. inhibiting hormones
  • anterior pituitary gland produces many hormones related to development and growth; many have tropic effects, but many do not
    • growth hormones (gh): rbst
    • prolactin: lactation in the mammary glands
    • adrenocorticotropic hormone: adrenal cortex
    • follicle stimulating hormone and luteinizing hormone: reproductive glands
    • tsh, msh

adrenal glands

• coordinates short and long term stress responses
• above and adjacent to kidney glandss
• adrenal gland has two regions: the cortex (outer region) and the medulla (inner region)
• coordinates making atp, oxygen, increasing blood supplies
• short-term responses are coordinated by the medulla:
  • “fight or flight”; produces epinephrine and norepinephrine (nor/adrenaline)
  • two forms of bioenergetic boosts:
    • increases energy supplies for cells
      • targets liver cells and skeletal muscle cells: increases rate of glycogen conversion to glucose
      • targets adipocytes: increases release rate of fatty acids
      • culminates in increased production of ATP
    • increases oxygen and nutrient supplies
      • targets lung cells: dilates bronchioles and increases respiratory rates
      • targets cardiac muscle tissue: increases heart rate and stroke volume
        • heartbeat increases; contractions increase stroke volume
        • blood pressure rises
      • targets smooth muscle: selective vasoconstriction and vasodilation in blood vessels
        • blood is recirculated to where blood is most necessary: dilates in the head, skeletal muscles; constricts in skin, digestive system, kidneys, urogenital tract/reproductive system
  • adrenal medulla secrets epinephrine and norepinephrine
    • enters bloodstream and binds to receptors on liver and skeletal muscle cell membranes
    • non-steroid hormone
    • g-protein to adenylyl cyclase to cyclic amp to camp dependent protein kinase to enzyme kinase to enzyme → releasing production
    • amplified
    • phosphorylase breaks chemical bonds in glycogen, producing glucose
    • makes available glucose
  • brain neurons propagate signals to the adrenal medulla to secrete epinephrine and norepinephrine
    • autonomic nervous system has two branches: sympathetic and parasympathetic
      • sympathetic stimulates, parasympathetic restores
      • sympathetic branch initiates the short-term stress response
    • sympathetic motor neuron passes synaptic cleft and propagates signal to adrenal medulla endocrine cells
    • binds and stimulates
    • acetylcholine is neurotransmitted
• long-term stress responses illustrated over multiple hours in the cortex
  • corticotropin releasing hormone enters through portal vein to anterior pituitary gland; induces release of ACTH (adrenocorticotropic hormone)
  • adrenal cortex receptors stimulate secretion of glucocorticoids and mineralocorticoids
  • glucocorticoids: a group/category of hormones; mammalian/vertebrates primarily use cortisol
    • cortisol targets skeletal muscle cells: desynthesizes muscle proteins for amino acids to help produce new glucose and produce new ATP
    • cortisol targets adipocytes: releases fatty acids to produce new glucose and produce new ATP
    • amino acids and fatty acids are transported to the liver cells to synthesize new glucose for ATP production
    • increases blood glucose levels
  • mineralocorticoids: another group; primary is aldosterone
    • aldosterone targets kidney nephrons: modifies nephrons to increase sodium ion reabsorption, which increases water reabsorption
      • water follows salt; osmolarity
      • water reabsorption increases the blood volumee
    • changes blood volume; blood volume is proportional with blood pressure, so mineralocorticoids try to increase blood pressure and increase efficiency of circulation
  • immunosuppression
  • long-term trade-off of resources towards other systems: expensive
  • anti-inflammatory properties of glucocorticoids: hydrocortisone suppression of histamines (antihistamines)
• cortisol is also produced daily: standard production increases rhythmically and peaks, coinciding with alertness and productivity vs. melatonin production

excretory system

• kidneys and nephrons, bladders and tubules
• eliminate nitrogenous waste as excretory fluid; osmoregulation and homeostasis
• excretion breaks down amino acids, proteins, and nucleic acids and isolates nitrogenous bases
  • toxic waste (esp. from amino acids and proteins) in bloodstream
• initially transformed into ammonia waste product; many animals excrete as is
  • many convert ammonia into urea or uric acid
• most aquatic animals and amphibians excrete ammonia
  • small molecule
  • high water solubility
    • toxicity level easily diluted in water, but must have a lot of external/internal water supply
  • high toxicity
  • low energy requirement to excrete; no conversion required
  • only larval stage amphibians excrete ammonia
• mammals, sharks, and adult amphibians excrete urea
  • mostly terrestrial
  • avoids coating self or air in ammonia
  • 100,000x lower toxicity
  • ammonia and co2 → urea; occurs in liver
  • still high water solubility; must be dissolved in water, but needs lower supply
  • higher energy requirement due to hepatic conversion
  • sharks excrete urea due to saline environment; excreted as an osmoregulation adaptation; some urea is kept in the tissues to maintain balance
• birds, insects, and many reptiles (terrestrial/aerial invertebrates) excrete uric acid
  • low toxicity
  • insoluble in water; dissolves out, paste/crystalline; needs very little water to be excreted
  • best in water-limited environments or for animals with reproductive constraints towards water
  • high metabolic conversion from ammonia to uric acid; more expensive than converting to urea
  • while egg layer/shelved juveniles have a lot of water, birds and reptiles excrete due to reproductive constraints
    • shelled amniotic eggs vs. non-shelled; uric acid would not intoxicate egg yolk due to insolubility
    • instead, a membrane known as the allantois stores the nitrogenous waste in compact form before the newborn hatches, preventing poison
• urinary system/excretory system composed of the kidneys, the renal veins and arteries, the ureter, and the bladder
  • direct connection to the descending aorta and the posterior vena cava
    • disproportionate amount of blood sent to kidney; 1% of body weight or less
    • many capillaries associated with kidney (renal organs)
  • urine forms in kidney and excreted through two sided tubules: ureter
  • ureter carries down to bladder; a storage tank
    • bladder sphincter allows excretion of urine through the urethra
• kidney composed of the renal cortex and renal medulla (endocrine system)
  • millions of nephrons are contained densely in the medulla; 50mi
  • nephrons produce urine
  • urine is drained out of the nephrons into the central region of the kidney; the renal pelvis
  • renal pelvis is a collection area which drains into the ureter tubule
• nephrons have five major regions; many of the products and waste are filtered through the blood, so there are many blood vessels and capillaries at each nephron
  • materials are constantly reabsorbed from the pre-urine and returned through fluids and the bloodstream to the body
  • blind-ended tubules
    • blind end: renal corpuscle
      • blood is filtrated for most materials
      • two distinct parts
      • the wall is the Bowman’s capsule
      • thin blood vessels insert through the Bowman’s capsule through the lumen into a central capillary bed known as the glomerulus
      • the glomerulus produces the pre-urine
      • another blood vessel is inserted into the capsule so blood can flow out of the blind-end
      • a filtrate;; the pre-urine is left in the lumen and carried out of the renal corpuscle
      • remember the blood remains in a closed circulatory system
        • blood pressure forces blood through the system; fluid and solutes small enough to pass the glomerulus capillary wall pores will be pushed out into the lumus of the Bowman’s capsule
          • pre-urine/filtrate forms made from water, electrolytes, urea and nitrogenous waste, and small nutrients (glucose, vitamins, amino acids)
            • ions, waste, small nutrients
            • nephrons sort through filtrate to isolate urea and return as much of the remaining filtrate as possible
            • about 25% of water in your blood is removed in the renal corpuscle: ~180L of pre-urine is formed in one day, and about 99% of this water is reabsorbed to the body
          • size-selective filtration defines very small filtration; large components that should stay in the blood stay in the blood (erythrocytes and leukocytes, blood proteins)
          • passive, not active process enforced by blood pressure
    • proximal tubule
      • water and various solutes removed from proximal, loop of henle, and distal tubule; differs based on section
      • first modification of composition and volume of pre-urine and secretion of more solutes into the pre-urine
        • hydrogen ions and ammonia are secreted into the pre-urine as needed to balance the pH of the urine so it balances to ~6-7 pH average (slightly acidic)
        • reabsorption begins: water and various solutes are reabsorbed in the proximal tubule
          • various electrolytes begin to be reabsorbed into the body for physiological processes
          • various nutrients are reabsorbed at the proximal tubule: vitamins, amino acids, and glucose
            • nearly all glucose is reabsorbed at the proximal tubule
          • water begins to be reabsorbed into the body through aquaporins in the walls of the tubule: water channels in the nephron that allow osmosis into the external interstitial fluid to travel to the blood
    • Loop of Henle: a loop which dips from the renal cortex into the renal medulla with a descending and ascending limb
      • in the descending limb, water permeates the wall, but solutes cannot permeate it
        • the concentration of the interstitial fluid outside of the loop of henle is always greater than inside regardless of where it is relative to the renal medulla or cortex, so water will permeate through the loop due to osmosis
      • activity of the ascending limb and the collecting duct creates an osmotic gradient
      • at the ascending limb, the permeability inverts; sodium and chlorine ions are permeable
        • ascending limb has a thinner part which eventually broadens out for the distal tubule when reentering the renal cortex
        • ions in the thin lower section have a high enough concentration relative to the interstitial fluid that it diffuses out into the fluid; passive diffusion
          • high solute concentration applies in general to renal medulla; concentration gradient exists for sodium and chloride
        • concentration gradient inverts at thicker portion of the ascending limb; there are more ions outside than inside the limb
          • remaining ions are pumped out through active transport
        • sodium-chloride ion diffusion is largely responsible for the osmotic gradient in the renal nephrons and drawing out water from the descending limb
    • distal tubule
      • affected by the endocrine system: adh and aldosterone hormones regulate tubule proceses
      • electrolytes and sodium ions are reabsorbed via active transport
      • more water is reabsorbed as concentration of interstitial fluid increases
        • aldosterone influences the amount of salt secreted, so more water is reabsorbed
          • water is reabsorbed as needed; aldosterone is produced as needed
    • collecting duct
      • sodium and chloride ions actively transported out for reabsorption
      • some urea is reabsorbed to maintain the osmotic gradient
        • the very end of the collecting duct is permeable to urea
        • urea is reabsorbed to keep gradient; final addition
      • water is reabsorbed as needed
      • any pre-urine left at the collecting duct is the final urine product
      • collecting duct flows into renal pelvis into ureter into bladder into urethra
  • osmotic gradient in kidney
    • interstitial fluid: bathes cells/tissues
    • the interstitial fluid osmolarity increases with the depth of descent into the renal gland; the renal medulla has more saline concentrated in solute/higher osmotic fluid than the renal cortex
    • antidiuretic hormone is secreted from the brain to the collecting duct and binds to the specific receptors
    • increases amount of aquaporins and permeability/leakiness of wall; increases water reabsorption
    • adh increases when blood osmolarity is too high; when body is dehydrated
  • aldosterone secretes in kidney nephrons via an alternate process to adrenal cortex (long-term stress) in endocrine system
    • still increases blood pressure in a different form
    • RAAS: Renin-Angiotensin-Aldosterone System
    • sensory receptors near the glomerulus for blood pressure; activated by low blood pressure levels
      • low osmolarity
      • bleeding; open wounds
      • dehydration
      • diarrhea
    • kidney cells release renin enzyme
    • renin enzyme activates angiotensin II peptide
    • activated angiotensin II acts as a hormone with two effects:
      • vasoconstriction: blood pressure rises
      • targets adrenal cortex: secrete aldosterone
      • aldosterone targets distal tubule and collecting ducts
        • targets distal tubule: increases permeability of walls to sodium ions; reabsorption of sodium increases
          • water follows salt; reabsorption of water increases
          • blood volume increases → blood pressure increases

reproductive system

• related to anterior pituitary gland
• gonadotropin releasing hormone (GnRH)
• both male and female go through the same processes, but the effects are different
  • the hypothalamus secretes gonadotropin releasing hormones
  • gonadotropin releasing hormones travel through portal vessels to the anterior pituitary glandd
  • the pituitary gland secretes luteinizing hormones and follicle stimulating hormones
    • males:
      • luteinizing hormones target the leydig cells in the testes: releasing hormones which produce testosterone
      • follicle stimulating hormones target the seminiferous tubules in the testes to initialize facet of sperm production
      • testosterone and follicle stimulating hormones stimulate tubules and produce sperm
      • additional testosterone stimulates development of secondary sex characteristics
• statistics for male and female reproduction
  • male
    • each testes has 500ft seminiferous tubules which produce sperm daily
    • avg 300mil sperm produced per day
    • 50 million to 300 million sperm is ejected per ejaculation
    • infertility is considered less than 20 million sperm per ejaculation
    • unused sperm is broken down and reused; macrophages consume the broken down debris and it is replaced by new sperm
    • sperm lives for ~48 hours on average and up to 4-5 days within the female reproductive tract
  • female
    • follicles (immature eggs) are made during meiosis and begin to erode at birth; 2 million on average are present upon time or erosion
      • → about 40,000 follicles remain when puberty begins
      • female eggs are larger investment
    • about 6-7 follicles mature and are lost during menstrual cycle; only one is ovulated in one cycle
    • about 400 eggs are ovulated in one lifetime
    • eggs are viable for only 24 hours following ovulation; every month, only ~24 hour period where female can get pregnant

female reproductive cycle

• two concurrent cycles
  • ovarian: ovary
  • menstrual: uterine
• four week cycle
  • follicular phase/menstruation: days 1–7
    • follicular phase in ovarian cycle
      • follicle develops in the ovary; oocyte develops
      • secondary oocyte; not yet an egg until maturation
      • follicle possesses follicle stimulating hormone receptors; fsh stimulates and causes follicle growth
        • lh has no present effect on follicle
      • low levels of estradiol and progesterone concentration
        • amount of estradiol is important to cycle: different effects dependent on levels of estradiol in system; low levels inhibit, high levels positively stimulate hypothalamus and anterior pituitary gland
    • menstruation
      • endometrium (uterine layer) is shed
  • days 8–13: continued follicular phase/endometrium
    • follicular phase
      • follicle grows receptive of luteinizing hormone
      • follicle grows larger and begins to secrete estradiol; noticeably increased levels of estradiol, peaks at end of week
      • day 13: hypothalamus and anterior posterior gland are stimulated to produce more gonadotropin releasing hormone in the hypothalamus → anterior posterior gland produces more follicle stimulating hormone and luteinizing hormone; FSH and LH largely spike
    • growth of endometrium
      • high level of estradiol acts on endometrium
      • endometrium thickens in preparation for fertilized egg
  • ovulation occurs on ~day 14
    • spike in luteinizing hormone from ~day 13 causes ovulation
      • ovulation prediction kits based on spike in luteinizing hormones
      • most likely period for fertilization to occur
      • not a day, but a burst/moment in which ovulation occurs
        • sometimes can be felt in humans; ovulation can occur in different ovaries and can be felt
  • days 15–24: luteal phase
    • second half of both phases
    • levels of fsh/lh fall, estradiol levels out, progesterone level increases
    • “long third week”
    • remaining follicular tissue in the ovary transforms into the corpus luteum: glandular structure which secretes endocrine hormones
      • secretes high progesterone and moderate estradiol → inhibits the hypothalamus’s ability to produce gonadotropic releasing hormones → low fsh/lh → no new follicle matured
      • continuation estradiol and progesterone build the endometrium wall for a fertilized egg; glands develop to supply nutrients to an embryo
  • days 25-28: end of luteal phase
    • low GnRH fails to maintain corpus luteum; corpus luteum disintegrates
    • cease estradiol/progesterone production
    • inhibition removed
    • arteries constrict, blood flow drops, endometrium disintegrates at end of cycle
    • repeat day 1
  • if fertilized: human chorionic gonadotropin produced by embryo
    • mimics progesterone to sustain the corpus luteum

vertebrates

• several shared derived characteristics of vertebrata
  • more than two sets of hox genes: four seen
    • resulted in increased evolutionary adaptations: complex nervous system and skeleton, vertebral column; additional copies of gene doing what they were supposed to as well as evolutionary advantages/novelties
  • endoskeleton made from either cartilage or bone with a hollow vertebral column and a cranium
    • vertebral column protects the spinal cord
  • neural crest cells form early in development in the embryo and migrate to other parts of the body to develop other parts of the vertebrate body plan: the skull, teeth, neurons, sensory organs in the face, etc.
• two groups: jawless and jawed vertebrates; refers to bite

jawless fish

• clade Agnatha
  • a-gnath
• evolved about 500 million years ago
• two extant classes: lampreys and hagfishes
• early agnathan fishes had wide diversity:
  • conodonts: large, suctioned, hingeless maw with mineralized “teeth”; prolific before extinction
  • jawless armored fishes: fish with bony plates and a less developed pharyngeal basket
    • first group to use gill structure exclusively for gas exchange, not filter feeding: gill slits, etc.
• lampreys (ammocoetes larva)
  • ectoparasitic fish
  • saliva contains anticoagulant; prevents host blood from clotting
  • anadromous: spend parts of time in fresh and saltwater
    • hatch in freshwater
    • swim downstream to saltwater for maturation
    • return to freshwater to reproduce
• hagfishes
  • deep ocean, ocean floor
  • scavengers: feed on decaying animals, detritus
  • copious amounts of slime used as protection
• agnatha lack jaws, scales, and paired fins
  • no paired fins at the anterior ventral and dorsal; only fins at the dorsal posterior
• agnatha have a prominent notochord which persists into adulthood
  • vs. replacement of notochord with jointed vertebral column

jawed vertebrates

• clade gnathostomata
  • hinged jaws evolved through serial macroevolution (basal gnathostomes to chondrichthyes and beyond)
  • homeotic genes related to the development of the gill bar mutated and duplicated
  • larger and hinged gill bars improved ventilation and filter feeding for early jawed vertebrates
    • became multifunctional
    • adapted for capturing prey
  • gill bars and jaws developed from ectoderm (gill arches), not mesoderm
  • hox gene molecular homologies in jawbones and gill arches
  • evolution from gill arches of filter feeding chordates

class chondrichthyes

• sharks, skates, rays
• flexible, lightweight cartilaginous endoskeletons
  • less dense
• planar fins: water moves differently above and below fins creating lift
• large livers and oil maintains buoyancy
• reduced notochord
• vertebrae
• placoid scales: ridged, non-overlapping
  • increased drag
  • shark teeth are modified placoid scales
  • constantly losing and regrowing teeth
• active predators and filter-feeders: manta-rays
• lateral line system
  • small pores (“black dots”) which open into a canal
  • base of canal possesses sensory receptors (hair cells)
    • analogous to inner ear hair cells
    • stimulate action potentials in neurons
  • modified electrosensory system is only in cartilaginous fish: concentrated in the snout and lower jaw
  • use in long-range navigation
• dioecious, ovoviviparous individuals
  • oviparity: egg layer
  • viviparity: live birth
  • ovoviviparity: no placenta, but egg yolk nourishes the fetus

bony fishes

• formerly class osteichthyes; paraphyletic
• notable evolutionary reduction/replacement of the notochord by the articulated (jointed) vertebral column
• ctenoid or cycloid scales; no placoid scales
  • larger scales vs. placoid; rounded
  • greater overlap
  • not developed for buoyancy: instead, swim bladder
• lateral line system without an electrosensory system
• mostly dioecious and oviparous reproducers; large group, many exceptions
  • broadcast spawning, little parental care
• high fecundity: high numbers of gametes and offspring produced during a single episode
  • female cod: 4-6 million eggs

actinopterygii

• ray-finned fishes

sarcopterygii

• collection of bones support the fins: large, fleshy, with dense collection of bones
  • …like tetrapods?
  • joints of the fins articulate with the pectoral and pelvic girdle
    • fish lobes are homologous to tetrapod limbs
• two common groups of sarcopterygii: coelacanths and lungfishes

immune system

• specific defenses: lock-and-key for a specific pathogen
  • repeat sicknesses/strains
• several barriers of defense
  • skin, when intact
    • slightly acidic: pH 5 or lower
    • nonhospitable for growth
    • openings in the skin lack barriers
  • mucus membranes on entry points of the body
    • respiratory tract, digestive system
  • liquid and other materials: saliva, tears, earwax, hair
    • protect non-mucus membrane-covered areas
    • saliva and tears are watery
  • gastric juice
    • highly acidic: pH 2
      • mix of enzymes and hydrochloric acid
      • follows esophagus point of entry: in the stomach
• non-specific defenses: general, non-discriminate immune system responses
  • bacteria, fungi, viruses
  • non-specific immune activity
  • natural killer cells
    • cells secrete chemicals that attack anything which emits a harmful signal
      • causes apoptosis
  • mast cells
    • connective tissue cells
    • exposure to environment
    • not leukocytes
    • cause vasoconstriction near the wound to reduce blood loss
    • releases histamines: cause vasodilation of general area: causes blood to flood to area to cause blood clotting: squeeze blood and prevent new pathogens from entering while blood does not flow out
  • 4 kinds of leukocytes
    • produced in bone marrow
    • not lymphocytes; other 4 kinds are found in the 2nd line of defense
    • neutrophils, eosinophils, basophils, and monocytes
      • neutrophils and monocytes are the most common leukocytes
      • phagocytic by nature (macrophages)
      • “cleanup cells”
    • note that monocytes mature into macrophages
      • large phagocytes that consume pathogens and debris: bacteria