anatomy exam 2 part 1

Main function of endocrine system

Regulate body processes using hormones as chemical messengers.

Role of hormones

chemical messenger released by a cells in one part of the body that affect cells in other parts of the body (travels through the blood)

Endocrine–nervous interaction

Nervous system detects changes; endocrine system releases hormones to adjust physiology.

What types of structures detect changes in our internal and external environment? Do those structures belong to the endocrine system or nervous system?

receptors that belong to the nervous system

Endocrine vs nervous communication

Endocrine: hormones, slow, long-lasting, widespread. Nervous: electrical signals, fast, short-lived, targeted.

Endocrine vs exocrine glands

Endocrine secrete hormones into blood; exocrine secrete substances through ducts.

Do all cells respond to hormones

No; only cells with specific receptors respond

Water-soluble vs lipid-soluble hormones

Water-soluble bind membrane receptors (hydrophilic)

• act quickly, short lived, ex) insulin, glucagon

Lipid-soluble bind intracellular receptors (hydrophobic)

• act slowly, long lasting, ex) cortisol, estrogen, T3, T4

Receptors for hydrophobic hormones

Inside the cell because lipid-soluble hormones cross membranes.

action of hydrophobic hormones

Hydrophobic hormones bind to and activate receptors within cells.

The activated receptors alter gene expression, resulting in the formation of new proteins.

The new proteins alter the cell’s activity, causing the physiological response of the hormone

Receptors for hydrophilic hormones

On the cell membrane because water-soluble hormones cannot cross membranes.

action of hydrophobic hormones

The binding of a hydrophilic hormone to its membrane receptor sets off a cascade of events within the cell

hormonal interactions

The responsiveness of a target cell to a hormone may depend on the influences exerted by other hormones

• can have permissive effects, synergistic, or antagonist

Permissive effect

One hormone is necessary for another to produce an effect

• Enables another hormone to fully function

• ex) thyroid hormone enables epinephrine

Synergistic effect

Two hormones amplify a response (estrogen + progesterone).

Antagonistic effect

Hormones oppose each other (insulin vs glucagon).

Three ways hormone secretion is stimulated

• Neural: any input that activates neurons, triggering electrical or chemical signaling within the nervous system

• hormonal: release of a hormone triggered by another hormone

• humoral stimulation: regulation of hormone release in response to changes in the composition of bodily fluids, such as blood, including ion or nutrient concentrations.

Location of hypothalamus

In diencephalon; regulator of the endocrine system, controlling hormone production and maintaining homeostasis through its interaction with the pituitary gland.

Location of pituitary gland

Below hypothalamus; anterior pituitary secretes hormones, posterior stores/releases hypothalamic hormones.

Why posterior pituitary is neurohypophysis

hormones are produced in hypothalamus and travel down axons to posterior pituitary gland. action potentials from hypothalamus trigger release

• ADH

• Oxytocin

Why anterior pituitary is adenohypophysis

True glandular tissue that produces and secretes hormones.

Portal system

two capillary beds connected by veins; allows targeted hormone transport.

Hypophyseal portal system

Carries hypothalamic hormones to anterior pituitary to be released

Posterior pituitary hormones

ADH: target kidneys, increases BP

oxytocin: target uterus, increases contractions

both made in hypothalamus

Negative vs positive feedback

Negative reverses change; positive amplifies change.

seven anterior pituitary hormones

TSH, ACTH, GH, PRL, FSH, LH, MSH; target thyroid, adrenal cortex, liver/bone, mammary glands, gonads.

melanocyte stimulating hormone (MSH)

stimulated by: UV exposure and leptin

function: stimulates melanocytes to produce melanin, regulate energy balance

target organs: melanocytes

follicle stimulating hormone (FSH)

stimulated by: gonadotropin-releasing hormone (GnRH) from hypothalamus

function: stimulated follicle/ovum development and estrogen production, sperm development

target organs: ovaries (female), testes (male)

luteinizing hormone (LH)

stimulated by: gonadotropin-releasing hormone (GnRH) from hypothalamus

function: stimulated ovulation, androgen production

target organs: ovaries (female), testes (males)

prolactin

stimulated by: suckling of nipples

function: stimulates mammary gland formation in puberty, stimulated production of milk

target organs: mammary glands

growth hormone (GH)

stimulated by: growth hormone releasing hormone (GHRH)

function: stimulates release of growth factors from liver, breakdown of triglycerides in adipose tissues, enhances cellular proliferation

target organs: liver, bones, adipose tissue, nervous system cells, immune system cells

thyroid stimulating hormone (TSH)

stimulated by: TRH

function: stimulates release of thyroid hormones T3 and T4

target organs: thyroid gland

adrenocorticotropic hormone (ACTH)

stimulated by: corticotropin releasing hormone (CRH) from hypothalamus

function: stimulates release of cortisol and androgens from adrenal cortex

target organs: zona fasciculata of adrenal cortex

Releasing hormones function

Stimulate anterior pituitary secretion.

Inhibiting hormones function

Reduce anterior pituitary secretion.

Tropic hormones

Hormones that stimulate other endocrine glands.

Pineal gland

Located in epithalamus; secretes melatonin.

Function of melatonin

Regulates sleep–wake cycles.

Thyroid histology

Follicles filled with colloid; follicular cells surround colloid; parafollicular cells between follicles.

Follicular cells secrete

T3 and T4.

Parafollicular cells secrete

Calcitonin.

Functions of T3/T4

Increase metabolic rate, heat production, heart rate, oxygen consumption.

Most abundant thyroid hormone

T4 (90%); active form is T3 (10%).

Thyroid hormone solubility

Hydrophobic; transported bound to proteins.

how are thyroid hormones transported in the blood

Most thyroid hormones are attached to transport proteins

• Only free T3 can be utilized by the cells

Transport of iodide

Active transport into follicular cells.

Hypothyroidism

Low thyroid hormone; causes fatigue, weight gain, cold intolerance.

Hyperthyroidism

Excess thyroid hormone; causes weight loss, heat intolerance, tachycardia.

Primary vs secondary hypothyroidism

Primary: thyroid problem; secondary: pituitary problem.

Primary vs secondary hyperthyroidism

Primary: thyroid overactivity; secondary: excess TSH.

Goiter

Enlarged thyroid; often due to iodine deficiency or excess TSH.

Calcitonin

Lowers blood calcium; secreted by thyroid.

How calcitonin lowers Ca2+

Increases bone deposition; decreases osteoclast activity.

Parathyroid glands location

Posterior thyroid; secrete PTH when blood calcium is low.

Function of PTH

responds to low blood calcium, Raises blood calcium via bone resorption, kidney reabsorption, vitamin D activation.

Calcium homeostasis

Calcitonin lowers Ca2+; PTH raises Ca2+.

Why pancreas is endocrine & exocrine

Exocrine pancreas – (Acinar cells) release enzymes related to digestion

Endocrine pancreas – (Pancreatic Islets) responsible for controlling blood sugar

Pancreatic islets

Clusters of endocrine cells; alpha cells produce glucagon, beta cells produce insulin.

Hyperglycemia

High blood glucose.

Hypoglycemia

Low blood glucose.

How insulin lowers glucose

Increases uptake into cells; stimulates glycogen formation.

How glucagon raises glucose

Stimulates glycogen breakdown and gluconeogenesis.

Insulin + glucagon homeostasis

Opposing hormones maintain stable blood glucose.

Diabetes mellitus

Chronic hyperglycemia due to insulin issues.

Type I vs Type II diabetes

Type I: no insulin production; Type II: insulin resistance.

Normal fasting blood glucose

About 70–99 mg/dL.

Gestational diabetes cause

Pregnancy hormones from placenta cause insulin resistance; usually resolves after birth.

(hypothalamic-pituitary adrenal) HPA axis stimulus

Stress (physical, emotional, metabolic) triggers hypothalamus → CRH → pituitary → ACTH → adrenal cortex → cortisol

Effect of cortisol

Increases glucose, suppresses immune system, helps stress response.

Adrenal cortex hormones

Mineralocorticoids, glucocorticoids, androgens.

Adrenal medulla hormones

Epinephrine and norepinephrine.

Zona glomerulosa

Outer layer; secretes aldosterone (mineralocorticoids)

Zona fasciculata

Middle layer; secretes cortisol (glucocorticoids)

Zona reticularis

Inner layer; secretes androgens

Mineralocorticoids

steroid hormones that regulate electrolytes; main one is aldosterone. increase reabsorption of Na in kidneys

Glucocorticoids

steroid hormones that regulate metabolism and stress; main one is cortisol. increases rate of protein catabolism. cushings syndrome/addison’s disease

Main androgen

testosterone

Aldosterone

Increases sodium retention and potassium excretion.

Aldosterone & blood pressure

Raises blood volume via kidney sodium retention.

renin-angiotensin-aldosterone system (RAAS) pathway

renin → angiotensinogen → angiotensin I → ACE converts it into → angiotensin II.

what is RAAS stimulated by

low blood volume or low Na+ concentration stimulate renin

ACE

Converts angiotensin I to II.

ACE inhibitor

Blocks angiotensin II formation; lowers blood pressure.

ADH

organ secreting: produced by hypothalamus but stored and released from the posterior pituitary gland

stimulus: high blood osmolarity (too much solute), dehydration, low BP, low blood volume, angiotensin II

target tissue: kidneys

function: absorption of water increases blood volume and BP

part of HPA axis

Atrial natriuretic peptide

organ secreting: atria (top chambers of heart)

stimulus: increased stretch on atrial wall due to increased blood volume or pressure

target tissue: kidneys

function: decrease sodium and water reabsorption, reduce blood pressure and volume

Renin

organ secreting: kidneys

stimulus: low BP

function: initiates RAAS

Erythropoietin

organ secreting: kidneys

stimulus: increased hypoxia in cells

target tissue: bone marrow

function: increase red blood cell production