Anatomy & Physiology Flashcards
What is the role of the endocrine system?
To keep body in a state of homeostasis, carries out communication and regulation in response to normal physiological changes in the body or alterations in the external environment
Endocrine System vs Nervous System
Endocrine is slow acting, nervous is fast acting
Endocrine works using hormones, nervous works using electrochemical impulse
Endocrine regulates activities requiring duration rather than speed, nervous regulates activity of muscles and glands
List all the hydrophilic hormones
Anterior pituitary FSH/LH, TSH, ACTH, GH
Posterior pituitary ADH, oxytocin
Thyroid - Calcitonin
Pancreas - Insulin, Glucagon
Parathyroid - PTH
Gonad - Inhibin
Placenta - hCG
Adrenal Medulla – Catecholamines (Epinephrine, Norepinephrine)
List all the hydrophobic hormones.
Adrenal cortex - Aldosterone, Cortisol
Gonad - Testosterone, Progesterone, Estrogen
Kidney - Vitamin D (Calcitriol)
Pineal - Melatonin
Thyroid - T3, T4
List all the protein and peptide hormones.
Anterior pituitary FSH/LH, TSH, ACTH, GH
Posterior pituitary ADH, oxytocin
Thyroid - Calcitonin
Pancreas - Insulin, Glucagon
Parathyroid - PTH
Gonad - Inhibin
Placenta - hCG
List all the steroid hormones.
Adrenal cortex - Aldosterone, Cortisol
Gonad - Testosterone, Progesterone, Estrogen
Kidney - Vitamin D (Calcitriol)
List all the amine hormones.
Adrenal Medulla – Catecholamines (Epinephrine, Norepinephrine)
Pineal - Melatonin
Thyroid - T3, T4
What are the parts of the pituitary gland?
Anterior pituitary
- Pars distalis
- Pars intermedia
- Pars tuberalis
Posterior pituitary (pars nervosa)
List the acidophils of the Pars distalis and what hormones they secrete respectively.
Somatotrophs - Growth Hormone
Mammotrophs - Prolactin
List the basophils of the Pars distalis and what hormones they secrete respectively.
Gonadotrophs– Follicle Stimulating Hormone , Luteinising Hormone (LH)
Corticotrophs– Adrenocorticotropin Hormone (ACTH aka corticotropin)
Thyrotrophs – TSH
What cells in the Pars intermedia secrete hormones? What hormones do they secrete?
Melanotrophs – Melanocyte stimulating hormone(MSH)
What are the cells in the Pars tuberalis?
Undifferentiated gonadotrophs
What are the features of note in the posterior pituitary gland?
Axons of neurosecretory cells in supraopticnucleus (SON)
Paraventricular nucleus (PVN) of hypothalamus
Pituicytes – sheets around nerve bodies
Herring bodies – contains granules storing ADH and oxytocin
List all the pituitary hormones that directly act on non-endocrine tissues
GH, Prolactin, ADH, Oxytocin
List all the pituitary hormones that when secreted, modulate the activity of other endocrine glands
TSH, ACTH, FSH, LH
What are the parts of the follicle
Follicular cells - synthesize thyroglobulin and secrete it into colloid
Colloid - extracellular space surrounded by follicular cells, site of thyroid hormone formation from thyroglobulin and iodine
Parafollicular cells - cells located in between the follicles, secrete calcitonin
Outline the process of thyroid hormone formation.
- follicle cells ER and GA produce thyroglobulin (TG), tyrosine incorporated into TG at the same time - exocytosis of tyrosine containing TG into colloid
- Thyroid caputres iodine from blood and transfers it into colloid via iodide Na K pump
- thyroperoxidase on follicle cell membrane before colloid oxidised the iodine to activate it
- iodine gets attached to the tyrosine to form MIT or DIT, MIT and DIT get coupled to form the thyroid hormones
- follicular cells endocytose from colloidal side to internalise part of the TG-hormone complex, lysosomes attack resulting vesicle to separate the iodinated hormones from TG
- Resulting T3 and T4 diffuse freely through follicular outer membrane to enter blood, quickly bind to plasma proteins due to high lipophilicity
- iodinase removes iodide from MIT and DIT for recycling of iodine
How are T3 and T4 metabolised?
T4 gets metabolised by 5-deiodinase to form T3 or r-T3
T4 (and T3 somewhat) also gets metabolised by conjugation with glucuronic acid in the liver, conjugate is secreted into bile and eliminated in faeces
How is thyroid hormone release controlled?
- low T3 & T4 triggers TSH secretion
- TSH binds to TSH receptor on follicular cells to start signalling, resulting in increased synthesis and secretion of thyroid hormones
- when T3 and T4 are secreted, triggers negative feedback loop to stop TSH and TRH secretion
What are the physiological effects of T3 and T4
- inc basal metabolic rate
- sympathomimetic effect
- cardiovascular effect
- bone growth and maturation
- development of nervous system in childhood
- normal CNS activity in adults
- increased synthesis and degration of proteins lipids and carbohydrates (depending on metabolic state)
How do T3 and T4 increase basal metabolic rate
increase size and number of mitochondria AND
increase number of enzymes regulating oxidative phosphorylation
therefore increases oxygen consumption and energy use under resting conditions
How do T3 and T4 exert sympathomimetic effect?
inc the proliferation of catecholamine (epinephrine & norepinephrine)target-cell receptors to increase target-cell responsiveness to catecholamines
How do T3 and T4 exert cardiovascular effect?
Increase heart’s responsiveness to catecholamines → inc HR and force of contraction → ↑CO
How do T3 and T4 help with bone growth and maturation
Stimulates growth hormone (GH) secretion and increases Insulin Growth Factor 1 (IGF-1) production by the liver
Promotes effects of GH & IGF-1 on synthesis of new structural proteins and skeletal growth
What would be the TH and TSH/TRH levels be like for hypothyroidism from primary failure of thyroid gland?
TH: low
TSH: high
Goiter present
TSH secreted but thyroid responds insufficiently/doesnt respond
What would be the TH and TSH/TRH levels be like for hypothyroidism from hypothalamic or anterior pituitary failure?
TH: low
TSH/TRH: low
Goiter absent
inability to secrete TSH/TRH
What would be the TH and TSH/TRH levels be like for hypothyroidism from lack of dietary iodine?
TH: low
TSH: high
Goiter present
TSH secreted and binds to TSH receptor, but not enough iodine to make TH
What would be the TH and TSH/TRH levels be like for Graves disease?
Hyperthyroidism
TH: high
TSH: low
Goiter present
TSI present
TSI binds to TSH receptor to stimulate TH release, which -ve feedbacks to result in low TSH and TRH, but TH continues to be released
What would be the TH and TSH/TRH levels be like for hyperthyroidism secondary to excess hypothalamic or anterior pituitary secretion?
TH: high
TSH/TRH: high
Goiter present
Excessive TSH/TRH results in overproduction of TH
What would be the TH and TSH/TRH levels be like for hypersecreting thyroid tumor?
Hyperthyroidism
TH: high
TSH: low
Overreaction to TSH resulting in high TH OR TH being produced even without TSH
How do the parathyroid glands regulate serum calcium?
Low serum Ca levels stimulates chief cells to secrete PTH
→ Inc osteoclastic activity in bones – Ca2+ release into blood
→ Increases calcium reabsorption in DCT of renal cortex
→ Indirectly increases the Ca absorption in the small intestine by stimulating Vitamin D absorption
What are the parts of the adrenal cortex?
Zona glomerulosa, zona fasciculata, zona reticularis
How can one discern the different parts of the adrenal cortex?
Zona glomerulosa: outermost layer, columnar/pyramidal cells in rounded/arched cords
Zona fasciculata: middle layer, long cords of large polyhedral cells, v spread out (vacuolated appearance)
Zona reticularis: innermost layer, smaller cells, irregular/tangled cords
What does the zona glomerulosa synthesise?
mineralocorticosteroids/aldosterone
What does the zona fasciculata synthesise?
glucocorticoids - cortisol
What hormone stimulates the zona fasciculata to secrete glucocorticoids?
ACTH
What does the zona reticularis synthesise?
Androgens - supplementary sex hormones
What do glucocorticoids do?
- decrease carbohydrate, protein and lipid metabolism (to prolong stores)
- suppress immune function
How can one find the adrenal medulla among the cortex?
- large pale staining polyhedral cells
- located further in from zona reticularis
- electron-dense granules (containing catecholamines)
What is the function of the adrenal medulla?
Trigger epinephrine and norepinephrine release for fight or flight response - innervated by preganglionic sympathetic neurons
Epinephrine: inc HR, dilate bronchioles, dilates arteries of cardiac & skeletal muscle
Norepinephrine: constricts vessels of the digestive system and skin, increasing the blood flowto the heart, muscles and brain
What is/are the function(s) of epinephrine?
Inc HR, dilate bronchioles, dilates arteries of cardiac & skeletal muscle
What is/are the function(s) of norepinephrine?
constricts vessels of the digestive system and skin, increasing the blood flow to the heart, muscles and brain
What are the types of cells in the Islets of Langerhans?
Alpha cells, beta cells, delta cells, PP or F cell
What hormones do the various cells in the Islet of Langerhans secrete?
Alpha cell: glucagon
Beta cell: insulin
Delta cell: somatostatin
PP/F cell: pancreatic polypeptide
What is the function of glucagon?
increases blood glucose content by triggering glycogenolysis and lipolysis
What is the function of insulin?
decreases blood glucose content by causing entry of glucose into cells
What are the functions of somatostatin?
- inhibits release of insulin and glucagon
- inhibits GH and TSH secretion from anterior pituitary
- inhibits HCl secretion from gastric parietal cell
What are the functions of pancreatic polypeptide?
- stimulate action of gastric chief cells
- decreases bile secretion, pancreatic secretion, bicarbonate secretion, intestinal motility
How is insulin release controlled?
- high levels of glucose detected by beta cells by glucose entering the cell via GLUT 2
- glucose in the cell stimulates an enzyme to phosphorylate it to become glucose-6-phosphate
- G6P enters Krebs cycle to release ATP
- ATP activates ATP-sensitive K channel to close, resulting in high intracellular K - depolarisation
- depolarisation stimulates voltage-gated Ca channel to open, causing Ca to enter the cell to act as secondary messengers - stimulates exocytosis of vesicles containing insulin
How does insulin decrease blood glucose?
Stimulates GLUT 4 translocation to the cell membrane in muscle and adipose tissue, so that they take in more glucose to use immediately or to store
Stimulates liver cells to store more glucose
How does glucagon increase blood glucose?
Mobilises energy-rich molecules from their stores
What are the functions of the testis?
Produce sperm, secrete testosterone
What are the functions of the epididymis and ductus deferens?
Serve as sperm’s exit route from testis, serve as site for maturation of sperm for motility and fertility, concentrate and store sperm
What are the functions of the seminal vesicle?
Supply fructose to ejaculated sperm, secrete prostaglandins that stimulate motility to help transport sperm within the male and female, provide the bulk of the semen and precursors for semen clotting
What are the functions of the prostate gland?
secretes alkaline fluid that neutralises acidic vaginal secretions, triggers clotting of semen to keep sperm in vagina during penis withdrawal
What are the functions of the bulbourethral gland?
secrete mucus for lubrication
Outline the process of testes descending.
- Testes descend from rear of abdominal cavity to the front to form 2 sides of scrotum
- usually completed by 7th month of gestation
What are the hormonal changes that lead to puberty in males?
Hypothalamus secretes GnRH in a pulsatile manner every 1-3 hours, which triggers the anterior pituitary to secrete LH and FSH
What does LH do in males?
Stimulates Leydig cells in the testes to secrete testosterone
What does FSH do in males?
Stimulates Sertoli cells in the testes to promote spermatogenesis
What does inhibin do in males?
Inhibits FSH secretion so that LH is selectively secreted, resulting in GnRH continuing to stimulate testosterone production without overdoing spermatogenesis
How is testicular function controlled?
- Hypothalamus secretes GnRH, which stimulates Anterior pituitary to secrete LH and FSH
- FSH acts on Sertoli cells, which secrete inhibin to exert -ve feedback on anterior pituitary to allow selective secretion of LH
- LH acts on Leydig cells, which secrete testosterone to exert negative feedback on hypothalamus and anterior pituitary to reduce LH secretion
What are the effects of testosterone?
→ Internal male genitalia differentiation
→ Increase in muscle mass
→ Pubertal growth spurt
→ Penis (growth)
→ Deepening of voice
→ Spermatogenesis
→ Libido
What are the effects of DHT?
→ External male genitalia differentiation
→ Sebaceous glands
→ Prostate (growth)
→ Male hair pattern
→ Male hair pattern baldness
How are the various forms of estrogen synthesised?
- aromatase is activated by FSH to convert androstenedione into estradiol
- estradiol initiates feedback loop to hypothalamus/pituitary gland
What does LH do in females?
triggers the creation of steroid hormones from the ovaries
What does FSH do in females?
aids in follicle growth & maturation and induces antrum formation (estrogenstorage)
What does inhibin do in females?
Inhibits FSH so that LH is selectively secreted, so that estrogen synthesis continues without overdoing follicle development
How is the ovarian cycle regulated?
- Rising levels of GnRH induces FSH and LH secretion
- inc estrogen acts on hypothalamus to inhibit GnRH secretion, and inhibin acts on pituitary to inhibit FSH secretion
- increased selective secretion of LH brings about differentiation of follicular cells into luteal cells and ovulation
- corpus luteum stimulated by LH to secrete estrogen and progesterone
- if no fertilisation, corpus luteum degenerates, resulting in no estrogen and progesterone production - negative feedback stopped, new follicular phase begins
How is the synthesis of estrogen controlled in the ovarian cycle?
- anterior pituitary secretes LH and FSH to develop follicle and get it to secrete estrogen
- secretion of estrogen negative feedbacks to decrease GnRH secretion, while secretion of inhibin selectively inhibits FSH secretion
Outline the uterine cycle.
→ Estrogen from corpus luteum causes onlyone oocyte to leave the ovaries
→ Oocyte travels through fallopian tube to the uterus, ruptured corpus luteum releases progesterone – uterine lining grows to prepare for potential embedding of a fertilised egg
→ If no fertilised ovule embeds, a few days later, corpus luteum stops secreting progesterone, resulting in estrogen and progesterone levels plummeting.
→ Drop in progesterone causes uterus to stop growing and maintaining uterine lining, causing uterine lining to be shed
→ Once period ends, ovaries get ready to rupture another follicle in the ovarian cycle to start both cycles again
What triggers puberty in females?
increased GnRH
What triggers menopause?
Decrease of hormone secretion - less follicles in ovaries results in lowered estrogen and progesterone secretion
What are the signs of menopause?
→ Cessation of menstrual cycles (12 months after last menstrual period)
→ Gradual atrophy of genital organs
→ Vasomotor changes (regulation of blood vessel dilation & constriction → hot flushes)
→ Skin changes
→ Psychological, emotional changes
→ ↑ cholesterol level – due to lower hormone synthesis
→ ↑ risk of osteoporosis (↓ bone mass due to less estrogen)
