Physiology Exam 4

Tubular secretion

Transfer of substances from peritubular capillaries into the tubular lumen

Molecules of tubular secretion

Hydrogen - Regulates acid base balance

Organic ions - Some transported bound to plasma proteins, anion and cation channels allow for secretion of variable products

Potassium secretion

Completely reabsorbed in the PT (Constant)

Secreted in the DT (Regulated) - Coupled to Na+ reabsorption via Na+/K+ pump, aldosterone

K+

stimulates adrenal cortex to release aldosterone

4 Digestive processes

Motility, secretion, digestion, absorption

Motility

Mix food and move it forward

Secretion

Water, electrolytes, organic constituents - enzymes, bile salts, mucus

Digestion

Hydrolysis of energy containing foods

Carbohydrates - turn polysaccharides and disaccharides into monosaccharides

Proteins - Peptides are broken down into amino acids

Fats - Triglycerides are turned into monoglycerol + 2 fatty acid chains

Absorption

Transporting small absorbable across GI wall

Motility and secretion regulation

Autonomous smooth muscle - Pacemaker activity and slow-wave potentials

Intrinsic nerve pleoles - Enteric nervous system is dedicated system to digestive system, contains sensory, inter, and motor neurons

Extrinsic nerves - ANS, SNS = decrease, PNS = increase

Gastrointestinal hormones - Release from portion of GI and produce excitation or inhibition in other regions

Receptor activation

Sensory signal that intiates reflex and hormonal pathways

Chemoreceptors

Detect chemicals in lumen

Mechanoreceptors

Detect stretch

Osmoreceptors

Detect changes in osmolarity

Components of GI tract

Mouth - Break up food, start digestion

Pharynx and esophagus - Move food

Stomach digestion

Small intestine - Digestion and absorption

Large intestine - Absorption of salt and water

Accessory organs - Pancreas, liver and gallbladder, and salivary glands

Mouth

Tastebuds

Teeth

Saliva

• Speech

• oral hygiene - Lysozyme lyses certain bacteria, HCO3- buffers acids that damage teeth

• Mucus lubricates food

• Begins carbohydrate digestion - Salivary amylase breaks down polysaccharides into maltose

Mouth regulation

Basal levels controlled by PNS

Simple reflexes occur when chyme or mechanoreceptors respond to food in mouth - salivary center in medulla - extrinsic ANS

Acquired reflexes no physical stimulation or receptors

Pharynx and Esophagus

Swallowing - Moving food from mouth to stomach

• Tongue pushes bolus to back or oral cavity - pharyngeal pressure receptors - swallowing center in medulla - sequential activation of muscles

• Peristaltic waves push food to stomach

Stomach

Oxyntic mucosa

• Exocrine secretions needed for digestion

  • Mucous or goblet cell - mucus

  • Chief cell - Pepsinogin

  • Parietal - HCl and intrinsic factor

Pyloric gland area

• Chemical signals regulate digestion

  • Enterocromaffin-like - Histamine

  • G cells - gastrin

  • D cells - Somatostatin

Digestion in stomach

HCl and pepsingogin/peptin

HCl

Activate pepsinogen - pepsin

Provide acidic environment for pepsin

Breakdown of CT and muscle fibers

Denature proteins

Kills additional microorganisms

Pepsinogen/pepsin

HCl cleaves small portion of molecule

Pepsin activates pepsinogen autocatalytic

Protein digestion by splitting peptide bonds

Intrinsic factor aids in absorption of VBR - RBC production

Regulation of Exocrine secretions of the stomach

ACH - stimulalatory

• NT from intrinsic nerve plexus in response to short reflexes of vagal stimulation

Gastrin - Stimulatory

• Endocrine signals from G cells in response to protein products in the stomach lumen and ACH

Histamine - Stimulatory to parietal cells only

• Paracrine signal released from ECL cells in response to. gastrin and ACH

Somatostatin - Inhibitory

• Paracrine signal released from D cells in response to acid

• Responsible for negative feedback of parietal, G, and ECL cells

Regulation of stomach emptying

Release chyme of small intestine via smooth muscle contractions of the stomach and opening of pyloric sphincter

• Fluid volume - Stretch of smooth muscle, intrinsic plexus via mechan receptors, gastrin production from stomach

Inhibit stomach opening = closing sphincter

• Fluid volume of duodenum - Fat, acid, hypertonicity, distention

• Regulation - Neural response, hormonal response

Emotions influence autonomic nervous system

What molecules are subject to tubular secretion?

Hydrogen and organic ions

4 steps food processing

Motility, secretion, digestion, absorption

4 ways GI tract motility and secretion are regulated

Basal levels controlled by PNS

mechanoreceptors respond to food in mouth - salivary center in medulla - extrinsic PNS

3 types of receptor activated by GI tract

Chemoreceptors, mechanoreceptors, osmoreceptors

List 4 components of saliva and function

Lysozyme lyses bacteria

HCO3- buffers acids that would break down teeth

Mucus lubricates food

Amylase breaks down polysaccharides into maltose

3 cells of oxyntic region and products

Mucous - mucus

Chief - pepsinogen

Parietal - HCl and intrinsic factor

3 cells of pyloric gland area and function

Enterocromaffin-like - Histamine

G cells - Gastrin

D cells - Somatostatin

Functions of HCl in stomach

Activate pepsinogen - pepsin

Provide acidic environment for pepsin

Breakdown CT and muscle fiber

Denatures proteins

Kills additional microorganisms

Function of pepsin in stomach

HCL cleaves small

Pepsin activates pepsinogen

Protein digestion by splitting peptide bonds

Intrinsic factor aids in absorption of VBR

Why pepsinogen

To prevent enzyme from digesting tissues of stomach

Autocatalysis

Enzymes catalyze their own activation

3 signals that stimulate secretions from stomach

ACh, gastrin, histamine

Pyloric gland hormone inhibits oxyntic mucosal secretions from stomach

Somatostatin