Topic 7 Flashcards
Endocrine system regulates 3 things..
growth, reproduction and metabolism
Endocrine glands and tissues secrete..
hormones which travel in blood to target cells (bind to receptors and change cell activity)
Receptor proteins found on either..
- cell membrane
- intracellular
2 types of hormone types
- water soluble
- lipid soluble
Water soluble hormones
peptides, proteins, catecholamines (1st messager)
Steps for a water soluble hormone
- hormone binds to cell membrane receptors (don’t enter cell for their actions)
- hormone receptor complex activates membrane proteins
- G proteins activates 2nd messenger systems
Example of cAMP as 2nd messenger
- hormone binds to cell surface receptor and activate g proteins
- g proteins activates adenylate cyclase (membrane protein)
- adenylate cyclase converts ATP to cAMP (2nd messenger)
- cAMP activates protein kinases
- protein kinase acts on the proteins to alter their activity
Why use 2nd messenger systems
- hormone can’t enter cell (water soluble)
- rapid acting (enzymes already present- just activate)
- 1 hormone molecule so many enzyme molecules activated so multiplies signal
- limited, messenger broken down or removed
Lipid soluble hormones
steroids and thyroid hormones, trigger protein synthesis so takes time therefore slow but long lasting
Steps for actions of the lipid soluble hormones
- enter target cell and bind to intracellular nuclear receptors in cytosol or nucleus
- hormone receptor complex binds to a specific region on DNA (Activates genes) starts gene transcription. produces mRNA
- mRNA attaches to ribosomes to produce proteins (translation)
Stimuli acting on an endocrine can be either ..
- humoral stimulus
- neural stimulus
- hormonal stimulus
Humoral stimulus
stimulus = ions/nutrients (something other than hormones)
Ex of humoral stimulus
increase blood glucose (after eating carbs): pancreatic B cells detect glucose and release insulin which lowers blood glucose
Neural stimulus example
1 heart rate: resting heart rate (surprise) –> SNS preganglionic directly to nt = ACh –> adrenal medulla (epineph. +NE) –> increase heart rate and force of contraction
Hormonal stimulus example (-‘ve feedback)
metabolism: low metabolism –> hypothalamus (thyrotrophin releasing hormone) –> ant. pituitary (thyroid stimulating hormone)–> thyroid gland (thyroxine T4) –> T4 to T3 –> increase metabolism
Stress
- any extreme external or internal stimulus
- triggers a set of body changes called general adaption syndrome
- all coordination directly or indirectly by the hypothalamus
Phase 1 of stress (Alarm Reaction)
(fight or flight). immediate =NS. CNS (sensory input- detect change) –> hypothalamus (RAS increase alertness) –> SNS –> organs or adrenal medulla –> epi and NE (prolongs response)
Effects of NS and hormones
- increase blood glucose (energy). SNS inhibits insulin release. epi, NE trigger conversion of glycogen to glucose in the liver
- increase HR, force of contraction
- decrease blood flow to skin, abdominal viscera so more available to skel and cardiac muscle and brain
- decrease digestion, urine production
Phase 2 of stress: resistance reaction
long term (endocrine) permits recovery from tissue repair OR response to longer term stress. hypothalamic hormones initiate phase 2
Growth hormone
stimulates growth
Cortisol
- release within 30 seconds of the stress but the response not for hours. steroid hormone, acts as nuclear receptors.
- inhibits insulin release
Release of hormones causes..
- increase blood hormone
- inhibition of immune system, bonds formation, formation of CT
- release aldosterone and antidiuretic hormone
increase blood glucose causes ..
- liver stimulated to produce new glucose from lots and later from proteins.
- little insulin so glucose not taken up well, special by skel. muscle and adipose tissue
- glucose spared for use by NS
- metabolism of non nervous tissue directed to fats for NRG
- if stress continues, cortisol inhibits GH release and proteins are then used
- overall increase blood FA and AA for energy
Release of aldosterone and antidiuretic hormone reduces..
salt and water loss at kidney to maintain blood volume
Long term effect of stress
decrease weight, increase bp, increase HR, immune suppression (cortisol) decrease bond density, increase risk of type 2 diabetes
Phase 3: exhaustion
results from depletion of body resources, loss of K+, damage to organs
Functions of testosterone
- development of organs of male reprod. tract of +2 sex characteristics
- stimulate bone growth at epiphyseal place (convert E to stop growth = closure of plate)
- promotes protein anabolism
- directly stimulates spermatogenesis
FSH
stimulates -1 to become 2 follicle, inhibited when increase progesterone (P) (so FSH increase when P decrease)
LH
- stimulates estrogen production from theca and granolas cells of follicle
- surge in LH therefor ovulation and formation of corpus luteum from remnants of follicle
- in follicular phase: E from 2 follicle rises for a few days then stimulus LH release then stimulus follicle to increase E secretion (+ve feedback) leads to LH surge
- luteal phase - P inhibits LH release
Estrogen
required for ovulation, development of 2 sex characteristics, stimulates growth, endometrium, increase bone growth, closure of epiphyses
Progesterone
from corpus lute, prepares uterus for pregnancy
Day 1-14 of ovarian cycle
Ovary: Follicular (preovulatory) phase
Early on: P low ∴ LH, FSH secreted - some 10 follicles → 20 follicles due to FSH
- follicles secrete E ∴ blood E rises
Later on: one (usually) 20 follicle becomes vesicular follicle
Day 1-14 of uterine cycle
Uterus:
i) Menstrual phase (days 1-5):
- stratum functionalis shed (outer layer of endometrium) + denuded areas bleed
∴ menstrual flow = blood, cells, secretions ii) Proliferative phase (days 6-14):
- E → repair + proliferation of stratum functionalis (due to mitosis in stratum basalis)
Day 14 of ovarian and uterine cycle
ovulation due to LH surge
LH triggers:
a) completion of meiosis I → 20 oocyte
b) rupture of vesicular follicle with release of 20 oocyte
Days 15-28 ovarian cycle
Ovary: Luteal phase
- high P from corpus luteum inhibits GnRH (∴ LH + FSH) ∴ no follicles develop
Days 15-28 uterine cycle
Uterus: Secretory phase
- P from corpus luteum:
i) prepares endometrium for implantation - becomes vascular, thick + stores glycogen
ii) inhibits uterine contractions
If fertilization occurs:
a) placenta secretes human chorionic gonadotropin (hCG)
- hCG maintains corpus luteum (similar structure to LH)
b) corpus luteum → P, E (for about 6 weeks, then placenta takes over (secretes P, E))
c) FSH, LH inhibited by high P (no new follicles develop)
If NO fertilization occurs:
a) corpus luteum → corpus albicans (no hCG, low LH)
b) ∴ P, E ⇓ ∴
i) no longer inhibit LH, FSH → LH, FSH ↑
ii) no longer maintain endometrium –> menstruation
3 types of contraceptives
- oral
- implants
- morning after pill
Oral contraceptives
high E + P → inhibit GnRH secretion ∴ low FSH, LH (mimics luteal phase) - no follicle maturation, no ovulation
Implants
e.g: progestin- similar mechanism to oral
Morning after pill
- high E and progestin or progestin only (= Plan B)
- prevents implantation, ovulation or fertilization
Placenta
- formed from chorion (fetus) and endometrium (maternal)
- blood vessels of mother and fetus close proximity (no blood mixing)
Placenta functions to..
1) exchange site:
- gases, nutrients/wastes, hormones, antibodies (passive immunity) - drugs e.g. alcohol, morphine, nicotine
- viruses - measles, polio
2) secretes hormones:
a) E + P
b) hCG
- maintains corpus luteum for ∼ 6 weeks post-fertilization - detected by pregnancy tests
- stim. testosterone secretion by fetal testes
