Physiology Exam 5

What is the primary function of the digestive system?

transferring molecules from external to internal environment

What are the 4 basic digestive processes?

motility, secretion, digestion, and absorption

Motility

muscular contractions of the digestive tract

What are the 2 types of motility?

propulsive and mixing

Propulsive motility

propel or push contents through the tract

Mixing motility

mixes food with digestive juices and exposes molecules to absorbing surfaces

Secretion

digestive juices are moved into the digestive tract by the exocrine glands

Digestion

biochemical breakdown of foodstuffs into absorbable units (monomers)

Absorption

movement of absorbable units, water, electrolytes, and vitamins from the digestive tract to the blood

What are the 2 divisions of the digestive system?

accessory digestive organs and the digestive tract

Accessory digestive organs

salivary glands, liver and gallbladder, exocrine pancreas

Digestive tract

oral cavity, pharynx, esophagus, stomach, small intestine, large intestine, anus

What are the 4 layers of the digestive tract?

mucosa, submucosa, muscularis, and serosa

Mucosa

protective surface that is specialized in some areas for secretion and absorption

Submucosa

connective tissue which allows for distensibility and elasticity

Submucosal plexus

regulates gut activity

Muscularis

smooth muscle that produces propulsive and mixing movements

Serosa

outer connective tissue that secretes fluid to prevent friction with surrounding viscera

What are the 4 factors that maximize digestion and absorption?

autonomous smooth muscle function, intrinsic nerve plexus, extrinsic nerves, gastrointestinal hormones

Autonomous smooth muscle function

some intestinal cells are pacemaker cells that continuously fluctuate membrane potentials

Intrinsic nerve plexus

networks of nerve fibers contained within the digestive tract

Extrinsic nerves

innervate digestive organs through the parasympathetic and sympathetic divisions

Gastrointestinal hormones

endocrine glands are located in various portions of the digestive tract

Smooth muscle cells

affects motility

Exocrine gland cells

secretion of digestive juices

Endocrine glands cells

secretion of hormones

What are the functional parts of the digestive system?

tongue and taste buds which stimulate salivary, gastric, pancreatic, and bile secretion

Secretion in the mouth

saliva begins carbohydrate digestion which facilitates swallowing

What is saliva production regulated by?

conditioned salivary reflex and autonomic influence

Pharynx and esophagus

uses propulsion motility move the bolus from the mouth through the esophagus to the stomach

What does mucus act as?

lubricant and a protective layer

What are the 2 stages of swallowing?

oropharyngeal and esophageal stage

Oropharyngeal stage

bolus moves from mouth through the pharynx to the esophagus through propulsive motility

Esophageal stage

bolus moves through esophagus to the stomach through propulsive motility

What are the 3 stomach regions?

fundus, body, and antrum

Fundus of the stomach

a thin muscle layer above the esophageal opening

Body of the stomach

thin muscle layer that stores food

Antrum of the stomach

thick muscle layer involved in mixing food

What are the 3 main functions of the stomach?

stores ingested food until emptied into small intestine, secretes hydrochloric acid and enzymes, and mixing motility pulverizes food and mixes with secretions

What do parietal cells secrete?

hydrochloric acid which activates pepsinogen

What do chief cells secrete?

pepsinogen

What does pepsinogen do?

converts to pepsin which initiates protein digestion

G cells

secrete the hormone gastrin in response to proteins in the stomach

Enterochromaffin-like cells (ECL)

release histamines which acts on parietal cells to speed up HCl secretion

D cells

release somatostatin which inhibits secretions by parietal cells, G cells, and ECL cells

Cephalic phase

thinking about smelling, or tasting the food before food arrives

Gastric phase

protein stimulates secretion of hormone gastrin which promotes secretion of HCl pepsinogen

Intestinal phase

inhibitory effects from small intestine which slows gastric secretion to regulate emptying

What are digested in the stomach?

carbs and protein

What can be absorbed in the stomach?

ethyl alcohol and aspirin can be but not food or water

What does the food mix with in the duodenum?

small intestine secretions, exocrine secretions, and liver secretions from bile ducts

What does the biliary system contain?

liver, gallbladder, and associated ducts

Proteolytic enzymes

digest proteins into small peptide chains and amino acids

Pancreatic amylase

digests polysaccharides into disaccharides

Pancreatic lipase

only secretion to digest fat

Aqueous alkaline secretion

neutralizes chyme and promotes pancreatic enzyme action

What are the functional parts of the small intestine?

duodenum, jejunum and ileum

Duodenum

does a lot of the digestion and absorption

Jejunum and ileum

finishes the process and aids in mixing

Segmentation of duodenum

initiated by distension from chyme

Segmentation of ileum

result of gastrin secretion from chyme goes into stomach

Migrating motility complex

when segmentation stops between meals and occurs after most absorption has occurred

Aqueous salt and mucus solution

provides lubrication and protection and provides H2O for hydrolysis

Na+ absorption

passive in between epithelial cells and active through epithelial cells

Vitamin absorption

mostly passive absorption

Electrolyte absorption

iron and calcium absorption are regulated

Carb and protein absorption

absorbed via secondary active transport into cells

Fat absorption

passively absorbed through micelles

Functional parts of the large intestine

cecum, colon, appendix, and rectum

Haustral contractions

slow mixing movements which shuffle contents back and forth

Mass movements

happens 3-4 times a day usually after meals where parts of the colon contract simultaneously

Anabolism

synthesis of larger macromolecules from smaller monomers which requires energy input

Catabolism

breakdown of macromolecules into monomers though hydrolysis and oxidation after anabolism if needed

Energy input

comes from ingested food and is released when molecule bonds are broken

Energy output

comes from the use of energy either through internal work or external work

External work

energy used to produce mechanical work

Internal work

activities necessary to sustain life

Essential nutrients only in food

amino acids, fatty acids, vitamin D and vitamin C

What stimulates hunger?

neuropeptide

What suppresses appetite?

melanocortins

Alpha cells

glucagon

Beta cells

insulin

What are the functional glands of the endocrine system?

pituitary, thyroid and parathyroid, adrenal, pancreas, gonads, thymus

Where do non-polar hormones bind to?

can pass through plasma membrane and bind to the receptor within the organ

Where to polar hormones bind to?

induce response through secondary messengers and bind to receptors on target organs

What is hormone secretion tightly regulated by?

negative feedback control, neuroendocrine reflexes, and circadian rhythm

Permissiveness

one hormone must be present in order for another hormone to be affective

Synergism

complementary actions of several hormones boosts their effects

Antagonism

one hormone reduces the effects of another

Posterior pituitary

functional and anatomically an extension of the hypothalamus which doesn’t produce hormones but stores vasopressin and oxytocin

Vasopressin

conserves water from nephrons and minimally controls arterial contraction

Oxytocin

contract uterine smooth muscle and promotes ejection of milk

Anterior pituitary

synthesizes hormones

Growth hormone

responsible for regulating body growth and metabolic actions

Adrenocorticotropic hormone

stimulates release of cortisol by the adrenal cortex

Luteinizing hormone (LH)

aids in control of sex hormone release and ovulation in females

Follicle-stimulating hormone (FSH)

aids in regulation of gamete production and reproductive function

Prolactin

enhances breast development and lactation in females

Thyroid hormone

regulates metabolic rate and calorigenic effect

Parathryoid glands

secrete calcitonin and parathyroid hormone