A&P Lab: Endocrine system

Catabolism

breaking down of complex materials (enzymes)

Anabolism

building of complex materials (enzymes)

Pure endocrine glands

• pituitary

• thyroid

• parathyroid

• thymus

• adrenals

• pineal

Mixed endocrine/exocrine

• pancreas

• gonads

• exocrine released via ducts

Hormones

• chemical substances secreted by cells into blood

• delay producing effects from seconds to hours

• prolonged effects

• amino-acid based or steroid hormones

• blood levels controlled by negative feedback systems

Humoral stimuli

• tropic hormones

• secretion of hormones in direct response to changing blood levels of ions and nutrients

• declining blood Ca2+ concentration stimulates parathyroid glands to secrete PTH (parathyroid hormone)

Nervous system modulation

• modifies the stimulation of endocrine glands and their negative feedback mechanisms

• can override normal endocrine controls

Hypothalamus

controls pituitary gland

Pituitary gland

• secretes 8 hormones, most control other hormones

• adenohypophysis (anterior lobe)

• neurohypophysis (posterior lobe)

Adenohypophysis

• anterior lobe of pituitary (glandular)

• hypophyseal portal system: vascular connection between hypothalamus and adenohypophysis

Neurohypophysis

• posterior lobe of pituitary (neural)

• hypothalamic hypophyseal tract: collection of axons from hypothalamus to neurohypophysis

Adenohypophysis hormones

• growth hormone (GH)

• prolactin (PRL)

• tropic hormones:

• thyroid-stimulating hormone (TSH)

• adrenocorticotropic hormone (ACTH)

• follicle-stimulating hormone (FSH)

• luteinizing hormone (LH)

Neurohypophysis hormones

• antidiuretic hormone (ADH or vasopressin)

• oxytocin

Growth hormone (GH)

• stimulates protein synthesis & use of fats for fuel, greatest effect of bone and skeletal muscle

• too much GH in childhood leads to gigantism or acromegaly in adults

• too little GH in childhood leads to pituitary dwarfism

Prolactin (PRL)

• in females: stimulate breast development, milk production, blood level rise towards end of pregnancy

• in males: stimulate testosterone production

Thyroid stimulating hormone (TSH)

• stimulates thyroid gland

• rising blood levels of TH act of pituitary and hypothalamus to block release of TSH

Adrenocorticotropic hormone (ACTH)

• stimulates adrenal cortex to release corticosteroids

• triggered by hypothalamic corticotropin-releasing hormone (CRH) determined by hypothalamus

• fever, hypoglycemia, and stressors triggers release of CRH

Gonadotropins

• regulate function of ovaries and testes (estrogen and testosterone production)

• triggered by hypothalamic gonadotropic-releasing hormone (GnRH) during/after puberty

• FSH

• LH

Follicle-stimulating hormone (FSH)

• regulate function of the ovaries and testes (estrogen and testosterone production)

• stimulates gamete (egg or sperm) production/ maturation

Luteinizing hormone (LH)

• regulate function of the ovaries and testes (estrogen and testosterone production)

• causes ovulation (turns the follicle into a corpus luteum in females)

• in males, stimulates testosterone production

Oxytocin

• stimulates smooth muscle contraction in breasts (milk ejection) and uterus (labor)

• synthetic and natural oxytocic drugs are used to induce or hasten labor (pitocin)

Antidiuretic hormone (ADH)

• regulates water volume and blood pressure

• directly affects water reabsorption (prevents urine formation)

• synthesized in hypothalamus

• alcohol can inhibit ADH release and cause copious urine output and dehydration (morning-after dry mouth)

Hypersecretion of ADH

• too much water retained

• edema, headache and disorientation

Hyposecretion of ADH

• diabetes insipidus

• excess urine output that’s not sweet (like diabetes mellitus)

• polyuria and polydipsia

Thyroid gland

• largest endocrine gland

• produces 2 hormones

• thyroid hormone (TH)

• calcitonin (thyrocalcitonin)

Thyroid hormone (TH)

• T3 - triiodothyronine

• T4 - thyroxine (common): glucose oxidation, regulate BMR, heat production, effect heart and nervous system

Calcitonin (thyrocalcitonin)

• decreases blood calcium by stimulating calcium salt deposit in bones

• antagonistic to parathyroid hormone

Hyperthyroidism

• glucose oxidation (weight loss and muscle wasting)

• increased BMR (increased appetite, weight loss)

• increased heat production (increased body temp and heat tolerance)

• rapid heart rate (cardiovascular system)

• irritability, restless, insomnia (nervous system)

Hypothyroidism

• common cause: lack of iodine

• glucose oxidation (decreased metabolism, stored as fat)

• decreased BMR (decreased appetite, weight gain)

• decreased heat production (decreased body temp, cold tolerance)

• low heart rate (cardiovascular system)

• mental dullness, depression (nervous system)

Parathyroid hormone (PTH)

• increases available calcium in blood by:

• releasing calcium from bone

• cause kidneys to reabsorb more calcium and less phosphate

• stimulate kidneys to convert vitamin D to calcitriol: increase calcium absorption from food)

• produced by chief cells

Hyposecretion of PTH

• causes neural excitability, can lead to:

• tetany- prolonged muscle spasms which can lead to respiratory paralysis

Hypersecretion of PTH

causes bone deformation, softening and spontaneous fractures

Adrenal cortex

• synthesizes and released steroid hormones called corticosteroids

• basic template for all steroid hormones: cholesterol

• mineralocorticoids

• glucocorticoids

• gonadocorticoids

Mineralocorticoids

• mainly aldosterone

• regulate Na+ reabsorption in tubules, indirectly regulate water reabsorption as “water follows the solute”

Glucocorticoids

• mainly cortisone, corticosterone and hydrocortisone (cortisol)

• increase blood glucose levels

Gonadocorticoids

• mainly androgens

• male sex hormones which are converted to testosterone or estrogen after release

• source of estrogen post menopause

Adrenal medulla

• releases epinephrine (80%) and norepinephrine (20%)

• neural stimuli: blood glucose levels rise, blood vessels to constrict, heart beat faster, blood flow increase to heart and skeletal muscle

Pancreas

• glucagon

• insulin

Glucagon

• stimulated by low blood glucose levels (hypoglycemia)

• major target is liver: promotes degradation of stored glycogen to release glucose into blood

• hypoglycemia caused by too much insulin (anxiety, nervousness, tremors, weakness and coma)

Insulin

• stimulated by high blood glucose levels (hyperglycemia)

• lowers blood glucose levels by: enhancing transport glucose into body cells, triggering enzymatic activity in cells that catalyzes the oxidation of glucose for ATP production, promoting liver to make glycogen

Diabetes mellitus (DM)

• caused by hyposecretion of insulin (type I) or ineffective insulin receptors (type II)

• inability of cells to use glucose and loss of glucose in urine

• 3 cardinal signs: polyuria, polydipsia, polyphagia

Type I diabetes mellitus

• autoimmune, beta-cell destruction, NO insulin formed

• must get insulin injections, lack of insulin causes DKA

Type II diabetes mellitus

• enough insulin, receptors not responding adequately

• patients generally obese and sedentary

• weight loss, healthy diet and exercise can return person to normal

Gonads

• females - ovaries: estrogen and progesterone

• males - testes: testosterone

Estrogen

• development of breasts and maturation of reproductive organs

• work with progesterone in cyclin changes in uterine lining and preparation of mammary glands for lactation

Progesterone

maintains uterine lining in quiescent state during pregnancy and works with estrogen

Testosterone

initiates maturation of reproduction organs, secondary characteristics and libido

Thymus and Pineal gland

• thymus: hormones direct maturation and specialization of T-cells (thymosin and thymopoietin)

• pineal (epiphysis cerebri): produces melatonin (inhibit precocious sexual maturation, creates drowsiness)