Study Guide 3

Exocrine glands

Secrete substances into ducts that empty onto skin or into a cavity (e.g., sweat, mammary, sebaceous glands)

Endocrine glands

Ductless glands that secrete hormones directly into the bloodstream (e.g., thyroid, pituitary)

Hypersecretion

Too much hormone being released

Hyposecretion

Too little hormone being released

Steroid/thyroid hormone mechanism

Lipid-soluble, pass directly through the membrane, bind receptors inside the cell/nucleus, require a transport protein in blood

Protein hormone mechanism

Not lipid-soluble; bind a membrane receptor (first messenger), triggering a second messenger (e.g., cAMP) inside the cell

Second messenger hypothesis

Protein hormone binds membrane receptor, generating an internal chemical (like cAMP) that modifies cell activity

Infundibulum

Stalk connecting the pituitary to the hypothalamus

Sella turcica

Depression in the sphenoid bone that holds the pituitary

Anterior pituitary (adenohypophysis)

Releases tropic hormones (e.g., GH, prolactin, FSH) in response to hypothalamic releasing/inhibiting hormones

Primary plexus

Capillary network where hypothalamic hormones enter before draining to the anterior pituitary

Growth hormone (GH) action

Stimulates target cells (bone, muscle, liver) to produce insulin-like growth factors (IGFs)

IGF effects

Increase amino acid uptake, promote lipolysis, promote glycogenolysis, spare glucose for neurons

Hypoglycemia response

Hypothalamus releases GHRH, anterior pituitary releases GH, liver releases IGF, glucose rises

Hyperglycemia response

Hypothalamus releases GHIH, GH is inhibited, no IGF release

Dwarfism (pituitary)

Caused by GH hyposecretion during childhood

Gigantism

Caused by GH hypersecretion during childhood, before epiphyseal plate closure

Acromegaly

GH hypersecretion in adulthood; causes enlarged extremities, jaw, and facial features

Posterior pituitary (neurohypophysis)

Stores and releases hormones (ADH, oxytocin) made by hypothalamic neurons

Antidiuretic hormone (ADH)

Decreases urine volume, causes vasoconstriction, promotes thirst; targets kidneys

Diabetes insipidus

Caused by ADH hyposecretion; symptoms include excessive urination and thirst

Oxytocin

Triggers uterine contractions, milk let-down, and is released during ejaculation ("love hormone")

Follicular cells (thyroid)

Secrete T3 (triiodothyronine) and T4 (thyroxine)

Parafollicular cells (C cells)

Secrete calcitonin

T3 vs T4

T3 has 3 iodine atoms, T4 has 4 iodine atoms

Effects of T3/T4

Increase basal metabolic rate, promote protein synthesis, increase Na+/K+ pump activity and heat production, upregulate beta receptors

TSH

Hormone from anterior pituitary that stimulates T3/T4 secretion

Thyroglobulin (TGB)

Protein made by follicular cells that iodine attaches to inside the follicle

Colloid

Material inside the thyroid follicle where TGB and iodine combine

Thyroxine-binding globulin (TBG)

Transport protein that carries T3/T4 in blood

Goiter

Enlarged thyroid caused by lack of iodine, since no T3/T4 means no negative feedback so TRH/TSH keep rising

Congenital hypothyroidism

In children, causes dwarfism and intellectual disability

Myxedema

Symptom of severe hypothyroidism; waxy facial appearance from subcutaneous fluid buildup

Hypothyroidism symptoms

Cold intolerance, weight gain, low blood pressure, slow heart rate, fatigue, dry skin

Graves' disease

Autoimmune hyperthyroidism where antibodies mimic TSH and overstimulate the thyroid

Hyperthyroidism symptoms

Weight loss, high blood pressure, increased heart rate, heat intolerance, anxiety

Exophthalmos

Eyes bulging outward, associated with Graves' disease

Calcitonin

Decreases blood calcium by increasing osteoblast activity and inhibiting osteoclasts

Parathyroid hormone (PTH)

Released when blood calcium is low; increases osteoclast activity, kidney calcium reabsorption, and calcitriol production

Calcitriol

Active vitamin D hormone that promotes calcium absorption from the gut

Adrenal cortex

Outer part of adrenal gland; secretes corticoids (mineralocorticoids, glucocorticoids, androgens)

Aldosterone

Mineralocorticoid released in response to low blood volume/pressure/sodium; increases sodium and water reabsorption in kidneys

Cortisol

Glucocorticoid ("stress hormone") that raises blood glucose via protein breakdown, lipolysis, and gluconeogenesis

Glucocorticoid anti-inflammatory effect

Suppresses WBC activity; chronic excess can suppress immunity

Cushing's syndrome

Caused by excess ACTH leading to elevated cortisol

Adrenal androgens

Produced by inner cortex zone; more significant for sex drive in females

Adrenal medulla

Inner part of adrenal gland; secretes epinephrine and norepinephrine for fight-or-flight response

Pancreatic islets

Clusters of hormone-secreting cells in the pancreas

Alpha cells

Secrete glucagon, which increases blood glucose via gluconeogenesis and glycogenolysis

Beta cells

Secrete insulin, which decreases blood glucose by increasing glucose uptake into cells

Insulin actions

Stimulates glycogen formation, fatty acid synthesis, amino acid uptake; decreases gluconeogenesis

Type I diabetes mellitus

Autoimmune destruction of beta cells; childhood onset; insulin-dependent (IDDM)

Type II diabetes mellitus

Adult onset; caused by down-regulation of insulin receptors; linked to obesity and inactivity

3 P's of diabetes

Polyuria, polydipsia, polyphagia

Diabetes complications

Neuropathy, slow healing, infections, DKA, heart disease/stroke, amputations

Estrogen (ovaries)

Prepares uterine lining for implantation, develops secondary sex characteristics

Progesterone (corpus luteum)

Maintains uterine lining for a fertilized egg

Testosterone (testes)

Develops male secondary sex characteristics

Thymosin

Hormone from the thymus that stimulates immune system development, larger in newborns

Melatonin (pineal gland)

Regulates sleep and mating cycles; increases with less light exposure