BIOG 1440 L18 — Struggles (Prelim Cram)

Animal hormones: misses, slips, and told answers from the Nov 7 Prelim 3 diagnostic. Same-session repair is not retention.

Write the HPA axis in order: each hormone and the structure that releases it.

Hypothalamus: CRH → anterior pituitary: ACTH → adrenal cortex: cortisol.

ACTH acts on which part of the adrenal gland?

The adrenal cortex (cortisol comes from the zona fasciculata), not the medulla.

What stimulates the adrenal medulla to release epinephrine?

Sympathetic nerves (autonomic nervous system), not CRH or ACTH.

Cortisol's negative feedback inhibits which two hormones?

CRH at the hypothalamus and ACTH at the anterior pituitary.

A cortisol-secreting adrenal tumor: predict CRH, ACTH, and cortisol, and explain cortisol.

CRH low, ACTH low, cortisol stays high. Feedback only lowers upstream signals, and the tumor ignores them.

Why does epinephrine act faster than cortisol?

Epinephrine's surface receptor changes existing proteins through transduction. Cortisol binds an intracellular receptor and changes gene expression, so new proteins must be made.

T3 and T4 feed back on which two hormones?

TRH at the hypothalamus and TSH at the anterior pituitary.

What converts T4 to T3, where, and which one is more active?

A deiodinase within cells. T4 is a prohormone; T3 is about 3–5 times more active.

What does the thyroid need iodine for?

To synthesize T4.

Iodine deficiency: predict T3/T4, TRH, and TSH.

T3/T4 low; TRH and TSH high, because feedback inhibition is lost (primary pattern).

Where are ADH and oxytocin made, and where are they released?

Made in hypothalamic neurons; stored in and released from the posterior pituitary. The posterior lobe does not produce them.

Which pituitary lobe do the HPT, HPA, and GH axes all use?

The anterior pituitary (TSH, ACTH, GH).

Define tropic hormone.

A hormone whose target is another endocrine gland, regulating that gland's hormone secretion.

Name the two anterior pituitary hormones the lecture gives as purely non-tropic, with their targets.

Prolactin (mammary gland) and MSH (melanocytes). Both act directly.

Are ADH and oxytocin tropic?

No. These posterior hormones act directly on physiological targets. Tropic describes function, not a lobe.

Name the anterior hormones that are tropic. Which one is both tropic and non-tropic?

TSH, ACTH, FSH, and LH are tropic. GH is both.

Prolactin versus oxytocin: which lobe releases each?

Prolactin: anterior, made there. Oxytocin: posterior, made in the hypothalamus.

Which two hypothalamic hormones control GH, and in which directions?

GHRH stimulates GH release. GHIH (somatostatin) inhibits it.

What are GH's direct (non-tropic) actions?

Fat breakdown and altered carbohydrate metabolism: blocks insulin's effect and raises blood glucose.

What is GH's indirect (tropic) branch?

GH → liver and other tissues release IGF-1 → growth, protein synthesis, and cell proliferation in skeletal and other tissues.

Name the three negative feedback effects in the GH axis.

GH and IGFs inhibit GHRH release, stimulate GHIH release, and inhibit GH synthesis and release.

Which pancreatic cell type makes insulin, and which makes glucagon?

Beta cells: insulin. Alpha cells: glucagon.

Name insulin's main actions on glucose.

Promotes uptake by cells and glycogen synthesis in the liver, lowering blood glucose.

Name glucagon's two actions that raise blood glucose.

Glycogen breakdown and gluconeogenesis (amino acids → glucose).

Are the insulin and glucagon loops positive or negative feedback?

Both negative: each returns blood glucose toward baseline.

Contrast type 1 and type 2 diabetes.

Type 1: autoimmune loss of insulin. Type 2: physiological dysregulation with reduced responsiveness to insulin.

Early in developing type 2, is insulin high or low? Why?

High (hyperinsulinemia): the pancreas compensates for insulin resistance.

Which adrenal zone makes aldosterone?

Zona glomerulosa of the adrenal cortex.

Where do ADH and aldosterone each come from?

ADH: hypothalamus, released from the posterior pituitary. Aldosterone: adrenal cortex. ADH is not an adrenal hormone.

Low cortisol, normal aldosterone, normal urination and electrolytes: why is this likely not Addison's?

Destroying the whole cortex would also lower mineralocorticoids, causing increased urination and abnormal electrolytes.

What single lesion explains low TSH and low ACTH together?

An anterior pituitary problem (possibly the hypothalamus). Ms. Doe had a pituitary tumor.

Low TSH and ACTH: how do TRH and CRH separate a pituitary fault from a hypothalamic one?

Pituitary fault: TRH and CRH high. Hypothalamic fault: TRH and CRH low.

Why does excessively low cortisol cause weight loss?

Low appetite and low blood sugar, which also means low insulin. Appetite falls: cortisol normally raises it.

Predict three effects of excess cortisol.

Higher blood glucose, more appetite, suppressed immune activity. Prediction from cortisol's taught actions, not a full disorder list.

What does cortisol break down to supply glucose? What breaks down glycogen in the stress response?

Cortisol: proteins, with amino acids converted to glucose. Epinephrine: glycogen, in the rapid arm.

Give the two general reasons one hormone can have different effects.

Different receptors, and different transduction pathways by cell type. Not different concentrations.

Epinephrine in liver cells: receptor and response?

Beta receptor; glucose release.

Epinephrine in vessels to skeletal muscle: receptor and response?

Beta receptor; smooth muscle relaxes, vessels dilate, blood flow rises.

Epinephrine in vessels to the digestive tract: receptor and response?

Alpha receptor; smooth muscle contracts, vessels constrict, blood flow falls.

Where are S cells, and what do they secrete?

In the duodenum (not the pancreas). They secrete secretin.

Trace the duodenal acid loop and name its feedback type.

Acid enters duodenum → S cells → secretin → pancreas releases bicarbonate → acidity falls. Negative feedback.

Trace the suckling loop and name its feedback type.

Suckling → hypothalamus → posterior pituitary oxytocin → mammary smooth muscle → milk ejection (not production) → more suckling. Positive feedback.