Lecture 2

Vocabulary flashcards covering hormonal and neural regulation of GI activity, intestinal motility, hypothalamic control of food and water intake, and anatomy, composition, formation, and regulation of saliva.

Endocrine regulation

Hormone released into the blood by a gland cell reaches distant target cells.

Neurocrine regulation

Neurotransmitter released from a neuron at a synapse acts on a post-synaptic neuron or effector cell.

Paracrine regulation

Chemical messenger diffuses through interstitial fluid to nearby target cells; local action.

Autocrine regulation

Messenger released by a cell acts back on the same cell that secreted it.

Enteroendocrine cell

Hormone-producing epithelial cell in stomach or small intestine that regulates GI functions.

Secretin

Peptide hormone from the small intestine that is involved in feedback control of GI activity.

Cholecystokinin (CCK)

Peptide hormone released by fatty acids & amino acids; stimulates pancreatic enzyme secretion and gall-bladder contraction.

Gastrin

Stomach peptide hormone involved in the gastric phase of GI control.

Negative feedback control (CCK example)

Absorption of fats & amino acids stops CCK release, ending the response it initiated.

Peristalsis

Coordinated contraction of circular muscle behind a bolus propelling contents toward the anus.

Segmentation

Alternating contractions in intestinal segments that mix chyme with enzymes and slow transit.

Pacemaker cells (GI)

Interstitial cells that generate spontaneous slow-wave depolarizations giving rise to basic electrical rhythm.

Slow waves

Rhythmic depolarization-repolarization cycles that set contraction frequency; require additional stimuli to reach threshold.

Basic Electrical Rhythm

Intrinsic electrical activity of GI smooth muscle determined by pacemaker slow waves.

Force of contraction (GI)

Proportional to the number of action potentials on a slow wave; modulated by neural & hormonal input.

Cephalic phase

GI reflexes initiated by sight, smell, taste, chewing, or emotions via parasympathetic nerves.

Gastric phase

Reflexes initiated by stomach distension, acidity, peptides; mediated by short (gastrin) & long (ACh) reflexes.

Intestinal phase

Reflexes triggered by intestinal distension, acidity, osmolarity, nutrients; mediated by secretin, CCK, GIP plus neural reflexes.

Hypothalamus

Brain region coordinating homeostasis, endocrine control, behavior; houses feeding & satiety centers.

Feeding center (lateral hypothalamus)

Region whose activation increases hunger; lesions cause anorexia.

Satiety center (ventromedial hypothalamus)

Region whose activation induces fullness; lesions cause obesity.

Orexigenic factor

Signal that increases food intake (e.g., neuropeptide Y, ghrelin).

Neuropeptide Y

Hypothalamic peptide that strongly stimulates hunger.

Ghrelin

Stomach hormone released during fasting; stimulates hypothalamic neuropeptide Y to promote eating.

Anorexigenic factor

Signal that decreases food intake (e.g., leptin, insulin, peptide YY, melanocortin).

Leptin

Adipose-derived hormone inhibiting neuropeptide Y release, reducing appetite and raising metabolic rate.

Insulin (appetite)

Pancreatic hormone that also signals satiety, lowering food intake.

Peptide YY

Intestinal hormone released after meals that suppresses appetite.

Melanocortin

Hypothalamic peptide reducing food intake.

Thirst center

Hypothalamic area regulating water intake.

Osmoreceptor

Hypothalamic receptor sensing plasma osmolarity; drives thirst and vasopressin release.

Vasopressin (ADH)

Hormone that conserves water at the kidney in response to high plasma osmolarity.

Renin-angiotensin system

Kidney-initiated pathway producing angiotensin II, which can stimulate thirst via the hypothalamus.

Parotid gland

Largest paired salivary gland; produces serous saliva rich in amylase.

Submandibular gland

Mixed serous/mucous salivary gland beneath the mandible.

Sublingual gland

Salivary gland under the tongue; mainly mucous secretion.

Saliva

Hypotonic, slightly alkaline secretion containing water, electrolytes, amylase, lipase, mucin, and antimicrobials.

Lysozyme

Salivary enzyme that lyses bacterial cell walls.

Lactoferrin

Salivary protein that binds iron, inhibiting bacterial growth.

Acinar cell

Salivary gland cell that produces isotonic primary secretion of saliva with enzymes and mucus.

Ductal cell

Salivary cell that reabsorbs Na⁺/Cl⁻, secretes K⁺/HCO₃⁻, making saliva hypotonic and alkaline.

Myoepithelial cell

Contractile cell surrounding acini & ducts that expels saliva toward the mouth.

Leaky tight junction (acinar)

Permits Na⁺ & H₂O movement paracellularly, keeping primary saliva isotonic.

Paracellular transport

Movement of substances between cells, as occurs for Na⁺ and water across leaky junctions.

Parasympathetic stimulation (salivary)

Dominant neural pathway increasing blood flow, protein secretion, and flow of saliva.

Sympathetic stimulation (salivary)

Minor pathway that also increases protein secretion and saliva flow.

Hypotonic

Having lower osmolarity than plasma; final saliva is hypotonic after ductal modification.

Alkaline

Having a pH above 7; saliva is made alkaline by HCO₃⁻ addition.

Amylase

Salivary enzyme that digests starch to disaccharides and trisaccharides.

Lipase

Salivary enzyme initiating fat digestion to fatty acids.