endocrinology

lab practical

chemical communication

composed of endocrine glands and hormones

endocrine glands:

• ductless and have rich blood supply

hormones:

• secreted into the bloodstream

• can travel to anywhere in the body and interact with any cell that has an appropriate receptor

  • hormone receptors are specific binding sites embedded in the cell membrane or located elsewhere in the cell

    • interacts with a particular hormone/class of hormones

types of hormonal stimulation

hormonal stimulation, humoral stimulation, & nervous system stimulation

hormonal stimulation

release of a hormone in response to another hormone

• i.e. anterior pituitary releasing thyroid-stimulating hormone (TSH) → TSH stimulates thyroid gland to release thyroid hormone (TH)

humoral stimulation

release of a hormone in response to changes in level of nutrient or ion in the blood

• i.e. blood glucose levels increase → stimulates pancreas to release insulin to lower blood glucose levels

nervous system stimulation

release of a hormone in response to stimulation by the nervous system

• i.e. sympathetic division is activated → sympathetic preganglionic axons stimulate adrenal medulla to release epinephrine & norepinephrine

comparison of nervous and endocrine system

mode of transport

• nervous: axon

• endocrine: blood

speed of response

• nervous: instant/milliseconds

• endocrine: delyated/seconds

duration of response

• nervous: miliseconds/seconds

• endocrine: minutes/days

for hormones concentration in blood determines strength of response

patterns of hormone secretion

chronic, acute & episodic (cyclic)

chronic hormone regulation

maintenance of relatively constant concentration of hormone

• i.e. thyroid hormone

acute hormone regulation

epinephrine response to stress

• very strong and quick

episodic (cyclic) hormone regulation

female reproductive hormones

factors that control concentration of hormones

• rate of secretion

• metabolic clearance rate (MCR)

  • rate of disappearance of hormone from plasma/concentration of hormone

regions of the hypothalamus

• Anterior portion → adenohypophysis

  • Stains much darker

• Posterior portion → neurohypophysis

  • Stains lighter

• Infundibulum: attaches pituitary gland to the hypothalamus

• In the hypothalamus

  • Paraventricular nucleus: produces the hormones that are stored in the pituitary gland

hypothalamo-hypophyseal portal system

portal system which connects the hypothalamus to the pituitary gland

• portal system consists of two capillaries

• transports and exchanges hormones

prolactin

anterior pituitary hormone

• stimulates milk production

  • target: breast

growth hormone

anterior pituitary hormone

• stimulates growth in childhood

• maintains healthy bone in adulthood

  • targets: skeletal system

adrenocorticotropin (ACTH)

anterior pituitary hormone

• stimulates production of cortisol

  • fights stress hormone— controls BP and sugar levels under stress

• targets: adrenal cortex on kidneys

thyroid-stimulating hormone (TSH)

anterior pituitary hormone

• regulates metabolism, energy balance, growth, and NS activity

  • targets: thyroid gland

luteinizing hormone (LH)

anterior pituitary hormone

• stimulates testosterone production in men

• stimulates ovulation in women

  • target: testes & ovaries

follicle-stimulating hormone (FSH)

anterior pituitary hormone

• promotes sperm production in men

• stimulates the ovaries to develop and estrogen production in women

  • target: testes & ovaries

melanocyte-stimulating hormone (MSH)

anterior pituitary

• stimulates melanin production → helps protect skin from UV rays

  • target: skin

anti-diuretic hormone (ADH, or vasopressin)

posterior pituitary hormone

• regulates water balance in body and sodium levels in the blood

  • target: kidneys

oxytocin

posterior pituitary hormone

• stimulates milk flow during breastfeeding

• promotes labour during childbirth

• promotes bonding between mother & child

  • target: breast & uterus

pineal gland

Pineal gland: secretes melatonin

• Controlled by the amount of light seen by the eyes each day

• Helps regulate the sleep cycle

• Pathway: light signals from eyes → suprachiasmatic nucleus of hypothalamus → pineal gland → pineal secretion

• made up of pinealocytes

Pinealocytes: manufacture melatonin in the absence of light and serotonin in the presence of light

Brain sand: calcified granular material located in the intercellular spaces

thyroid glands

• Located in the trachea of the neck

• Contains parathyroid glands

• Secretes triiodothyronine (T3): iodine-containing hormone

• Secretes thyroxine (T4) → eventually converted into T3

• Monitors metabolism

• regulated by thyroid-stimulating hormone (TSH)

Follicular cells: make thyroglobulin

Parafollicular cells: secretes calcitonin → decreases blood calcium levels

Parathyroid hormone secretes parathyroid hormone (PTH): releases calcium from the bones to be put into the bloodstream

adrenal gland

• Adrenal gland

  • Central area → adrenal medulla: secretes norepinephrine and epinephrine

    • Activated in response to stimulation by sympathetic preganglionic neurons

  • Zona glomerulosa: mineralocorticoids

    • Secretes aldosterone

      • Increases rate of sodium reabsorption by kidneys → increases sodium blood levels

  • Zona fasciculata: glucocorticoids

    • Secretes cortisol

      • Increases fat and protein breakdown

      • Increases glucose synthesis

      • Decreases inflammatory response

  • Zone reticularis: androgens

    • Weak androgen secreted → converted to testosterone by peripheral tissues

      • Stimulate public and axillary hair growth

      • Stimulates sexual drive in females

pancreas

• Pancreas

  • Releases both hormones and enzymes

  • Located close to the small intestine → releases enzymes into the small intestine

  • Alpha cells produce glucagon → stimulates the breakdown of glycogen into glucose and release it into the bloodstream 

  • Beta cells produce insulin → tells the liver to store glucose in the form of glycogen

  • Delta cells produce somatostatin → inhibits secretion of insulin and glucagon

graafian follicle

a mature ovarian follicle

• within the ovary

• following ovulation, becomes corpus luteum

  • secretes estrogen and progesterone

seminiferous tubules

produces mature sperm cells