BIO 431: Endocrine and Digestive Systems Review

Flashcards covering key concepts from Chapters 16 (The Endocrine System) and 23 (The Digestive System) for BIO 431 Human Anatomy & Physiology II.

How do the operational speed and response duration of the nervous system compare to those of the endocrine system?

Nervous impulses produce rapid responses occurring within milliseconds and having a brief duration, whereas endocrine hormones travel via blood, exhibiting a longer onset latency and an extended duration.

What is the physiological definition of a hormone?

A long-distance chemical messenger secreted into blood or lymph that regulates metabolic functions of target cells elsewhere in the body.

What is the functional difference between paracrine and autocrine chemical signals?

Paracrine signals act locally on neighboring cells within the same tissue without entering blood circulation, whereas autocrine signals exert their regulatory effects on the exact same cell that secreted them.

How do amino acid-based hormones and steroid hormones differ in lipid solubility and cellular signaling mechanisms?

Amino acid-based hormones are water-soluble (except thyroid hormone), cannot cross plasma membranes, and use second messenger systems (such as cAMP or PIP2-Calcium); steroid hormones are lipid-soluble, readily diffuse across plasma membranes, and bind intracellular receptors to trigger direct gene activation.

What are the three types of stimuli that trigger endocrine gland hormone synthesis and release?

Humoral stimuli (changing blood levels of ions or nutrients), neural stimuli (direct stimulation by nerve fibers), and hormonal stimuli (stimulation by tropic hormones released from another endocrine gland).

What anatomical and tissue distinctions differentiate the adenohypophysis from the neurohypophysis?

The adenohypophysis (anterior pituitary) consists of glandular epithelium that synthesizes and secretes hormones, whereas the neurohypophysis (posterior pituitary plus infundibulum) consists of neural tissue that stores and releases hormones produced by hypothalamic nuclei.

How do regulatory hypothalamic hormones reach the anterior pituitary versus the posterior pituitary?

Releasing and inhibiting hormones travel to the anterior pituitary via the hypophyseal portal system (a vascular network of capillary plexuses and portal veins), whereas posterior pituitary hormones travel down nerve axons via the hypothalamic-hypophyseal tract.

Which two hormones are stored in and secreted by the posterior pituitary, and what are their primary targets?

Oxytocin (targets the uterus and mammary glands) and Antidiuretic Hormone (ADH / Vasopressin, targets kidney collecting tubules).

What is a tropic hormone (tropin), and which anterior pituitary hormones belong to this category?

A tropic hormone regulates the secretory activity of another endocrine gland; anterior pituitary tropins include Thyroid-Stimulating Hormone (TSH), Adrenocorticotropic Hormone (ACTH), Follicle-Stimulating Hormone (FSH), and Luteinizing Hormone (LH).

What clinical conditions result from hypersecretion of Growth Hormone (GH) before versus after epiphyseal plate closure?

Hypersecretion before epiphyseal plate closure in children causes gigantism, whereas hypersecretion after epiphyseal plate closure causes acromegaly.

Which specific thyroid cells produce Thyroid Hormone ($\text{T}_3$ and $\text{T}_4$) versus Calcitonin?

Follicular cells produce Thyroid Hormone ($\text{T}_3$ and $\text{T}_4$), whereas parafollicular (C) cells produce Calcitonin.

How do Parathyroid Hormone (PTH) and Calcitonin antagonistically regulate blood $\text{Ca}^{2+}$ levels?

PTH (from chief cells) elevates blood $\text{Ca}^{2+}$ by stimulating osteoclast activity, enhancing renal $\text{Ca}^{2+}$ reabsorption, and activating Vitamin D; Calcitonin (from parafollicular cells) lowers blood $\text{Ca}^{2+}$ by inhibiting osteoclast activity at pharmacological doses.

What are the three distinct layers of the adrenal cortex, and what class of steroid hormones does each produce?

Zona glomerulosa produces mineralocorticoids (primarily Aldosterone), zona fasciculata produces glucocorticoids (primarily Cortisol), and zona reticularis produces gonadocorticoids (weak adrenal androgens such as DHEA).

What type of stimulus triggers catecholamine release from the adrenal medulla, and what are the primary secretions?

Neural stimulation by sympathetic preganglionic fibers triggers modified postganglionic chromaffin cells to secrete catecholamines ($80\%$ Epinephrine and $20\%$ Norepinephrine).

How do the microscopic anatomy and secretions of pancreatic acini compare to pancreatic islets (Islets of Langerhans)?

Pancreatic acini are exocrine structures that secrete enzyme-rich digestive juice and bicarbonate into ducts; pancreatic islets are endocrine cell clusters containing alpha and beta cells that secrete hormones (glucagon and insulin) directly into blood capillaries.

What are the antagonistic metabolic actions of Insulin and Glucagon on blood glucose homeostasis?

Insulin (from beta cells) is a hypoglycemic hormone that enhances glucose uptake, glycogen synthesis, and fat storage; Glucagon (from alpha cells) is a hyperglycemic hormone that stimulates glycogenolysis and gluconeogenesis in the liver.

What physiological mechanism causes polyuria in untreated diabetes mellitus?

Excessive blood glucose exceeds the renal reabsorption capacity, causing glycosuria and resulting in osmotic diuresis due to the osmotic draw of unabsorbed glucose in the kidney tubule filtrate.

What is the functional difference between peristalsis and segmentation in the alimentary canal?

Peristalsis is a propulsive process consisting of alternating waves of smooth muscle contraction and relaxation that squeeze food along the GI tract; segmentation is a nonpropulsive mechanical mixing movement in the small intestine that churns chyme back and forth.

What are the four fundamental concentric tissue layers (tunics) of the alimentary canal wall, from lumen outward?

Mucosa (lining epithelium, lamina propria, and muscularis mucosae), Submucosa, Muscularis externa (inner circular and outer longitudinal smooth muscle), and Serosa (visceral peritoneum) or adventitia.

Where is the myenteric nerve plexus situated, and what physiological activity does it control?

It is situated within the muscularis externa between the inner circular and outer longitudinal smooth muscle layers, where it controls gastrointestinal tract motility.

What is the function of the hepatic portal system in splanchnic circulation?

It collects nutrient-rich venous blood from the capillaries of the digestive viscera and routes it directly to liver sinusoids for metabolic processing and detoxification before entering the general circulation.

Which two substances are secreted by parietal cells in gastric glands, and what are their functions?

Hydrochloric Acid ($\text{HCl}$, which denatures proteins, activates pepsinogen, and kills bacteria) and Intrinsic Factor (which is required for intestinal absorption of Vitamin $\text{B}_{12}$).

What are the primary secretions of gastric chief cells?

Chief cells secrete pepsinogen (the inactive zymogen activated to pepsin by $\text{HCl}$) and gastric lipase.

Which three structural specializations increase the internal surface area of the small intestine for absorption?

Circular folds (plicae circulares), villi, and microvilli (brush border).

Where are Brunner's (duodenal) glands located, and what is the function of their secretion?

They are located in the submucosa of the duodenum and produce bicarbonate-rich alkaline mucus that neutralizes highly acidic gastric chyme.

What are the three vascular and ductal structures comprising a portal triad at the periphery of a liver lobule?

A branch of the hepatic artery proper, a branch of the hepatic portal vein, and a bile duct.

What is the non-enzymatic digestive role of bile salts released into the duodenum?

Bile salts physically emulsify large insoluble fat globules into millions of microscopic droplets, vastly increasing the surface area exposed to water-soluble pancreatic lipase.

What stimuli trigger the release of Secretin versus Cholecystokinin (CCK), and what are their primary target responses?

Acidic chyme triggers Secretin release to stimulate pancreatic duct cells to secrete $\text{HCO}_3^-$-rich juice and liver bile production; fatty/proteinaceous chyme triggers CCK release to induce gallbladder contraction and pancreatic acinar enzyme secretion.

How is inactive pancreatic trypsinogen converted into its active digestive form in the duodenal lumen?

It is cleaved into active trypsin by enteropeptidase (enterokinase), an enzyme bound to the duodenal brush border plasma membrane.

Compare the secretion source, optimal pH, and end products of Pepsin versus Trypsin.

Pepsin is secreted by stomach chief cells, functions optimally at $\text{pH } 1.5 - 2.5$, and hydrolyzes proteins into large polypeptides and small peptides; Trypsin is secreted by pancreatic acini, functions optimally at $\text{pH } 7.5 - 8.5$, and hydrolyzes proteins into small polypeptides and peptides.

Which enzymes hydrolyze carbohydrates in the mouth, small intestinal lumen, and brush border?

Salivary amylase (oral cavity, $\text{pH } 6.7 - 7.0$), pancreatic amylase (pancreatic acini, $\text{pH } 7.5 - 8.0$), and brush border disaccharidases (maltase, sucrase, lactase; $\text{pH } 7.0 - 8.0$), which break disaccharides into monosaccharides (glucose, fructose, galactose).

What are the distinct structural roles of micelles versus chylomicrons in dietary lipid absorption?

Micelles are water-soluble complexes of bile salts and fatty acids/monoglycerides that ferry lipid products to enterocyte microvilli for diffusion; chylomicrons are lipoprotein droplets assembled inside enterocytes that package resynthesized triglycerides for exocytosis into central lacteals.

Why does abrupt discontinuation of prolonged exogenous glucocorticoid therapy (prednisone) trigger an acute Addisonian crisis?

Exogenous prednisone exerts potent negative feedback on the hypothalamus (inhibiting CRH) and anterior pituitary (inhibiting ACTH), resulting in adrenal cortex atrophy; abrupt cessation leaves the atrophied cortex unable to synthesize endogenous cortisol, precipitating acute adrenal insufficiency.

Where are Peyer's patches located, and what is their histological classification?

They are aggregated lymphoid nodules located predominantly in the lamina propria and submucosa of the distal small intestine (ileum).