endocrine system

What types of stimuli control hormone secretion? Name examples

• Humoral stimuli: ions or nutrients in the blood that stimulate endocrine glands to secrete hormones

• Neural stimuli: neurons that stimulate endocrine glands to secrete hormones

• Hormonal stimuli: hormones from other endocrine glands stimulate other endocrine glands to secrete hormones

Name all the endocrine organs and their functions

• Hypothalamus

  • Adenohypophysis

  • Neurohypophysis

• Pineal gland

• Thyroid

• Parathyroid

• Thymus

• Pancreas

• Adrenal gland

• Gonads

How does the hypothalamus relate to the pituitary?

• Hypothalamus: regulates primitive functions of the body (ie water balance, thermoregulation, sex drive, childbirth)

• Pituitary gland/hypophysis: connected to hypothalamus by the infundibulum within sella turcica

What are the different parts of the pituitary? How are they embryologically different?

• Adenohypophysis/anterior pituitary gland: comes from the embryonic hypophyseal pouch from the pharynx

• Neurohypophysis/posterior pituitary: from the embryonic neurohypophyseal bud

What is the chain of command between the hypothalamus, pituitary gland, and other organs called? Name examples of these throughout the chapter.

• Axis: chain of command between hypothalamus-pituitary- target organ

  • (ie: hypothalamo-pituitary-thyroid axis)

Name the hypothalamic hormones that target the adenohypophysis and its general functions

• Thyrotropin-releasing hormone (TRH): secretion of thyroid-stimulating hormone (TSH)

• Corticotropin-releasing hormone (CRH): secretion of adrenocorticotropic hormone (ACTH)

• Gonadotropin-releasing hormone (GnRH): secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH)

• Growth hormone-releasing hormone (GHRH) / somatotropin-releasing hormone : promote secretion of growth hormone (GH)

• Somatostatin/growth hormone-inhibiting hormone (GHIH): inhibits secretion of GH and TSH

• Prolactin-releasing factor: promote secretion of prolactin (PRL)

• Prolactin-inhibiting hormone (PIH): inhibits secretion of prolactin

Name the secretions of the neurohypophysis and its targets and functions. Where did these secretions get

produced?

• Oxytocin (OT): Target the uterus and mammary glands to cause uterine contractions and milk release; maybe involved in ejaculation, sperm transport, sexual affection and mother-infant bonding

• Andiuretic hormone (ADH)/vasopressin: target kidneys and blood vessels for water retention and vasoconstriction, respectively

(both come from hypothalamus)

Where is the adenohypophysis located at? (don’t need to know pars tuberalis, pars intermedius)

Adenohypophysis: is the anterior ¾ of the pituitary gland with no nervous connection

What is the hypophyseal portal system?

Hypophyseal portal system: the hypothalamus secrete hormones into its…

• Primary capillaries of the hypothalamus that has portal venules that go down the infundibulum to

• Secondary capillaries within the anterior pituitary

Where is the neurohypophysis located at? What is it made out of?

Neurohypophysis: posterior ¼ hypophysis, made of nerve fibers and neuroglia, continuous with nerve fibers from hypothalamus via hypothalamo-hypophyseal tract

What attaches the hypophysis to the hypothalamus?

Infundibulum

Which hormones are produced by the adenohypophysis and what are their targets and functions? (don’t need to know MSH)

• Gonadotropins: target ovaries and testes

  • Follicle-stimulating hormone (FSH):

    • Female: stimulates ovarian estrogen, growth of ovarian follicles

    • Males: sperm production

    • PRODUCTION OF GAMETES

  • Luteinizing hormone (LH):

    • Female: ovulation, maintenance of corpus luteum + secretion progesterone

    • Males: testosterone secretion

    • PRODUCTION OF GENDER HORMONES
      
      

• Prolactin (PRL): target mammary gland and testes

  • Females: milk synthesis after birth

  • Males: increase LH sensitivity
    
    

• Thyroid-stimulating hormone (TSH)/thyrotropin: thyroid gland → release thyroid hormones and thyroid growth

  • REMEMBER TRH FROM HYPOTHALAMUS

• Adrenocorticotropic hormone (ACTH)/corticotropin: adrenal cortex → glucocorticoids (especially cortisol) for adrenal cortex growth
  
  

• Growth hormone (GH)/somatotropin: tissues + liver, bone, cartilage, muscle, fat → increase tissue growth and cellular differentiation

Which hormones are stored in the neurohypophysis and what are their targets and functions? Where is it produced?

• Antidiuretic hormone (ADH):

  • Target kidneys → increase reabsorption of water in kidneys

  • Target blood vessels → vasoconstriction but usually in pathological state

• Oxytocin (OT): increases during sexual arousal and orgasm causing satisfaction and emotional bonding

  • Females: target uterus and mammary glands → uterine contraction and stimulates milk flow

  • Males: propel semen

What does the pineal gland do? What hormone does it release and its function?

• Pineal gland: circadian rhythms (sleep cycle)

  • Melatonin: made at night and secreted in response to daylight

    • May cause suppression of gonadotropin (removing causes premature sexual maturation)

    • May cause puberty

    • In animals it causes seasonal breeding cycles

What is the thymus? What is the size of this in fetus vs adult? What do the hormones do? (don’t need to know specific hormone names)

• Thymus: involved in endocrine, lymphatic, and immune systems

  • larger in fetus than in adult
    
    

  • Matures T cells for immunity

  • development of other lymphatic organs

  • development and activity of T cells

What is the thyroid gland and what parts is it made of?

Thyroid gland: contains a isthmus that join the two lobes

What is colloid and its function? What are follicular cells and its function? What are parafollciular cells and its function?

• Colloid: rich in protein for hormone production

• Follicular cells: simple cuboidal epithelium that secrete thyroid hormones

  • T4 /Thyroxine/tetraiodothyronine: mostly produced, contains 4 iodine (needs to be converted to T3 in target cells)

  • T3 /Triiodothyronine: contains 3 iodine

• Parafollicular cells/C (clear) cells: calcitonin, between thyroid follicles

What do T4 and T3 do? What does calcitonin do, some of its targets, and when is it released?

• T4 and T3: increases metabolic rate, increasing oxygen consumption, generate heat

• Calcitonin: decrease blood Ca2+, antagonist of PTH released during hypercalcemia

  • Inhibits osteoclast activity and to help build bone (little effect in adults)

What is the function of parathyroid gland and its location? What are the targets and function of parathyroid hormone and under what condition is it released?

• Parathyroid glands: usually 4 on posterior side of the thyroid, contains many parathyroid cells

• Parathyroid hormone (PTH): increase blood Ca2+, antagonist of calcitonin released during hypocalcemia

  • Bone resorption in bones

  • Ca2+ reabsorption in kidneys

  • Increase calcitriol production

    
    

    
    

Calcitonin vs. Parathyroid Hormone (PTH)

Lowering Calcium vs. Increasing Calcium

Stop Bone Breakdown vs. Bone Breakdown

What are the two general regions/layers of the adrenal gland and their locations? Within the more superficial region, what are the 3 specific regions/layers and the hormones they produce?

• Adrenal medulla: inner gland

• Adrenal cortex: outer gland

  • Zona glomerulosa: thin layer located beneath adrenal capsule, circular cells, outer

    • mineralocorticoids regulating electrolytes

  • Zona fasciculata: thick layer with cells arranged in parallel cords with blood capillaries, middle

    • glucocorticoids regulating glucose and other organic fuels metabolism and sex steroids for developmental and reproductive functions

  • Zona reticularis: thin layer with branching network, inner

    • glucocorticoids

What is the function of the adrenal medulla? What hormones are released by the adrenal medulla?

What is the function of the adrenal cortex?

• Adrenal medulla: both an endocrine gland and ganglion of sympathetic nervous system and secretes

  • Epinephrine: ¾ of hormones released

  • Norepinephrine: ¼ of hormones released

  • Dopamine: trace amounts

• Adrenal cortex: produces corticosteroids/corticoids from cholesterol and contains 3 layers

What is the function of epinephrine and norepinephrine? What are some of its target cells?

Epinephrine/norepinephrine

• Increase alertness

• Increase heart rate, blood pressure, increase circulation to muscles, increase respiratory rate and increase metabolic rate

• Inhibit digestive and urinary systems

• Mobilize high energy fuels (ie: fatty acids, lactate and glucose)

• Liver increases glucose levels by glycogenolysis and gluconeogenesis

• Glucose-sparing effect by inhibiting insulin secretion

What are the three types of corticoids?

• Mineralocorticoids

• Glucocorticoids

• Sex steroids

Name a type of mineralocorticoid and its target cell and function. What layer/region produces this?

Aldosterone: zona glomerulosa, kidneys retain Na+ and secrete K+ for water to be reabsorbed to increase blood volume and pressure

Name a type of glucocorticoid and its target cell and function. What layer/region produces this?

• Cortisol/hydrocortisone: zona fasciculata and zona reticularis in response to ACTH pituitary →f at and protein catabolism, gluconeogenesis, increasing blood glucose and fatty acids

  • Adapts to stress and repair damaged tissues

  • Anti-inflammatory

  • May impair immune system

Name two types of sex steroids and its target cells and functions. What layer/region produces these?

• Androgens: made by zona fasciculata and zona reticularis

  • Develops male reproductive tract in fetus

  • Pubic and axillary hair and apocrine glands

  • Simulate libido (sex drive)

• Estrogen: made by zona fasciculata and zona reticularis

  • Estradiol: main adrenal estrogen (overshadowed by ovarian estradiol)

    • Increase skeletal growth and sustain bone

What types of cells are found in the pancreas and its functions?

• Acinar cells: produce exocrine digestive secretion

• Pancreatic islets/islets of Langerhans: endocrine function for regulating blood glucose

  • Alpha (α)/A cells: secrete glucagon to raise blood glucose

  • Beta (β)/B cells: secrete insulin to decrease blood glucose

  • Delta (δ)/D cells: secrete somatostatin/growth hormone- inhibiting hormone decreasing digestion

  • PP/F cells: secrete pancreatic polypeptide decreasing digestion

What hormones does the pancreas produce, its target cells, and its functions?

• Glucagon (targets liver and adipose mainly)

• Insulin (targets most cells, but mainly liver, skeletal muscles and adipose tissue)

• Somatostatin (targets stomach, intestines, and pancreas)

• Pancreatic polypeptide (targets pancreas, gallbladder, stomach)

Function of Glucagon?

• Liver to undergo glycogenolysis and gluconeogenesis to release glucose to blood

• Adipose tissue to catabolize fat and release free fatty acids

• Increase aa levels allow gluconeogenesis to occur

• Antagonist with insulin

Function of Insulin?

• Cells to absorb glucose, fatty acids, and amino acids to store or metabolize, lowering blood glucose

• Storage of nutrients by synthesizing glycogen, fat, and protein

• Increase cell growth and differentiation

• Antagonist with glucagon

Function of Somatostatin?

• Inhibits digestive enzyme secretion

• Inhibits nutrient absorption

• Maybe modulates pancreatic secretion of glucagon and insulin

Function of Pancreatic polypeptide?

• Inhibits gallbladder and intestinal contractions

• Inhibits release of bile and pancreatic digestive enzymes

• Inhibits release of gastric HCl

What are gonads?

What is each gonads’ exocrine vs endocrine functions?

• Gonads: Ovaries and testes have both exocrine and endocrine functions

  • Exocrine: produces eggs and sperm

  • Endocrine: produces sex hormones

What cells/structures are in the ovary? What hormones are produced by which cells/structure, its targets and functions?

• Ovaries

  • Theca cells

    • Androstenedione: is converted to estrogens by granulosa cells

  • Granulosa cells that produce

    • Estrogens: targets many tissues

      • Functions

        • Causing female reproductive development and adolescent growth

        • Regulate menstrual cycle and pregnancy

        • Prepares mammary glands for lactation

    • Inhibin: targets anterior pituitary to inhibit FSH secretion

  • Corpus luteum

    • Progesterone: targets uterus and mammary glands

      • Regulates menstrual cycle and pregnancy

      • Prepares mammary glands for lactation

    • Inhibin: targets anterior pituitary to inhibit FSH secretion

What structures are found in the testes? What do these structures produce? What are their target cells and

functions?

Testes

• Seminiferous tubules

  • Sperm

• Interstitial cells/cells of Leydig\

  • Testosterone: targets many tissues

    • Cause fetal and adolescent male reproductive development

    • Musculoskeletal growth

    • Sperm production

    • Libido

• Sustentacular/Sertoli cells

• Inhibin: targets anterior pituitary to inhibit FSH secretion

What does the skin produce?

keratinocytes of epidermis produce cholecalciferol from UV radiation which the liver converts into calcidiol

What does the kidney produce, its target organs and functions?

• Calcitriol (vitamin D3): converts calcidiol into calcitriol to raise blood calcium for bone deposition

  • Increase calcium absorption of small intestine

• Renin: from JG cells converting angiotensinogen to angiotensin I which is converted to angiotensin II by ACE to cause vasoconstriction

• Erythropoietin: 85% of it comes from the kidneys targeting red bone marrow to produce erythrocytes

What does the heart produce, its target organs and functions?

atrial natriuretic peptide (ANP) from atria and brain natriuretic peptide (BNP) from ventricles targets kidneys cause Na+ excretion causing water to follow, increase urine output, decrease blood volume and pressure