A+P Unit 5 Exam Prep

digestive system functions

• ingest food and fluids

• mechanically break down food

• propel solids and liquids

• digest nutrients

• absorb nutrients

• defecate

deglutition definition

swallowing, movement of food out of mouth and inferiorly through esophagus into stomach

buccal phase

• voluntary

• esophagus is closed, tongue presses against hard palate

• food is forced into a bolus toward the oropharynx

pharyngeal phase

• involuntary

• tongue pushes food back into oropharynx

• uvula and soft palate close off nasopharynx

• esophagus opens

• epiglottis closes off larynx

esophageal phase

• involuntary

• bolus is now in esophagus

• muscles of the pharynx contract to move bolus inferiorly into esophagus (peristalsis)

• superior esophageal sphincter closes to prevent emesis

• inferior esophageal sphincter opens and bolus enters the stomach

emesis is induced by

chemoreceptor trigger zone and vomiting center of medulla

• CTZ - senses chemical irritants and tells vomiting center to initiate vomiting

  • neurons from vestibular apparatus of the ear send signals to CTZ, causing motion sickness

anticipatory nausea

when emotional brain centers (ex. repulsive smell or sight) act directly on vomiting center

anti-emetic drugs do what

bind to CTZ receptors to block signals to the vomiting center and GI tract

stomach cells

• surface mucous cells

• parietal cells

• chief cells

• G-cells

parietal cells secrete

intrinsic factor and HCl

chief cells secrete

pepsinogen and gastric lipase

G-cells (enteroendocrine cells) secrete

ghrelin and gastrin into the blood

components of gastric acid

• hydrochloric acid

• intrinsic factor

• pepsinogen

• gastric lipase

hydrochloric acid

helps pepsin work, kills bacteria

intrinsic factor

glycoprotein required for vitamin B12 absorption, needed for erythrocyte production

pepsinogen

enzyme that breaks down proteins

gastric lipase

enzyme that breaks down fats

gastrin

• hormone released by G cells in mucosal layer of stomach in response to peptides, stretch receptors in stomach, lower stomach pH

• enters the blood, inducing histamine production and contraction of muscles in stomach and small intestine

ghrelin

• produced by stomach when empty

• regulates insulin secretion by pancreas and tells the body it’s time to eat

• regulated by ANS

goblet cells

produce mucous for lubrication and protection

enteroendocrine cells secrete

CCK and secretin hormones

CCK

• stimulates gallbladder contraction and pancreatic enzyme secretion

• inhibits gastric emptying

secretin

• reduces gastric acid secretion

• promotes bicarbonate and bile secretion

paneth cells

secrete lysozyme

segmentation of small intestine

local constriction of enzyme that mixes food with digestive juices

peristalsis in the small intestine

propulsion of food that involves alternating waves of contraction and relaxation

what happens in the duodenum of the small intestine

nutrient breakdown

what happens in the jejunum of the small intestine

nutrient absorption

what happens in the ileum of the small intestine

absorption

intestinal juice

secreted by pancreas in response to acidic chyme from stomach

lipid digestion and absorption

• lipids are emulsified into smaller fat droplets by bile salts

• pancreatic lipases (enzymes) hydrolyze triglycerides into monoglycerides and free fatty acids

• these pieces assemble into small fat droplets = micelles

• micelles diffuse into intestinal cells

• repackaged into smaller packages = chylomicrons

• transported away from intestine by lymphatic system

large intestine functions

• excretes wastes

• fluid absorption

• bacterial action

• feces formation

• defecation

ascending colon purpose

bacterial action and fluid reabsorption

vermiform appendix of large intestine

houses good gut bacteria

haustra of large intestine

• pockets along colon

• mix residue and help with water absorption

transverse colon purpose

fluid absorption

descending colon purpose

begins process of stool formation/storage

sigmoid colon purpose

stool storage

anus purpose

sphincter that relaxes to allow defecation

defecation reflex

• rectum contents stimulate baroreceptors in rectal wall

• increased nerve signals relayed by sensory neurons to the spinal cord

• increased nerve signals relayed along parasympathetic motor neurons

• smooth muscle of sigmoid colon and rectum contract, squeezing contents; internal anal sphincter relaxes

• conscious decision to defecate is controlled by cerebral cortex; external anal sphincter relaxes and Valsalva maneuver is initiated, eliminating feces

• requires relaxations of both internal (involuntary) and external (voluntary) sphincters

liver purpose

blood filtration and processing

portal triad

• bile duct

• branch of hepatic portal vein

• branch of hepatic artery

central vein

pulls processed, deoxygenated blood from hepatocytes

gallbladder purpose

stores bile for later use (with dissolved cholesterol)

common hepatic duct

drains bile to cystic duct and gallbladder for storage

common bile duct

drains bile to small intestine for later use

bilirubin

yellow waste product of heme breakdown

stercobilin

bilirubin breakdown product that gives feces brown color

pancreas purpose

glucose balance in blood

pancreatic exocrine function

pancreatic juice production by acinar cells

pancreatic endocrine function

production of insulin and glucagon by islet cells

pancreatic juice is made up of

• enzymes (amylases, lipases, nucleases)

• bicarbonate

absorptive state

ingested nutrients enter bloodstream from GI tract

postabsorptive state

GI tract is empty of nutrients and body’s own stores must supply energy

sympathetic nervous system impact on digestive activity

inhibits it

parasympathetic nervous system impact on digestive activity

enhances it

CCK

• released by duodenal cells in response to fatty chyme from the stomach

• cause contraction of gallbladder to release bile into duodenum

• inhibits gastric emptying and stomach secretions

secretin

• released by duodenal cells in response to acidic chyme

• stimulates liver, pancreas, and intestine to release more bicarbonate (adjust pH)

• inhibits secretion of HCl by stomach

leptin

• produced by visceral fat stores

• protects against weight loss in times of nutrient deprivation, but does not protect against weight gain

• obesity causes leptin resistance

ghrelin

• produced by endocrine cells of GI tract

• hunger hormone

• helps prepare for food intake by increasing stomach motility and secretion

• activates pituitary neurons to initiate appetite

• involved in energy homeostasis

orexins

• hormones produced by hypothalamus

• increase hunger/feeding and activity of RAS

macronutrients

• required for normal body functions

• make up most of what we eat

• includes

  • carbohydrates

  • proteins

  • fats

carbohydrates purpose

provide energy

proteins purpose

• provide structural support

• act as enzymes, antibodies, and some hormones

fats (lipids) purpose

• make up cell membranes

• cushion organs and some hormones

micronutrients

• necessary for our survival, but in smaller amounts

• includes

  • vitamins

  • minerals

  • water

nutrient pools

• current stocks of nutrients

• can be interconverted

• liver, adipose tissue, and skeletal muscles determine these levels and conversions

amino acid pool

• built by

  • tissue/protein breakdown

  • diet

• used for

  • protein synthesis

  • gluconeogenesis

  • fat storage

carbohydrate pool

• built by

  • diet

  • fat breakdown

  • protein breakdown

• used for

  • energy (ATP) production

  • excess fat storage

  • cholesterol production

  • cell membranes

GIP (gastric inhibitory polypeptide)

• induces beta cells to secrete insulin in fed state

• stimulate glucagon secretion at lower glucose levels in fasting state

• reduce acid secretion of stomach

• slow rate of gastric emptying of food into the duodenum

glucose sparing

• increased use of noncarbohydrate fuel sources and conservation of glucose

• occurs during prolonged periods without food

• brain needs glucose but other organs switch to fatty acids

  • lipolysis continues in adipose tissues

  • liver oxidizes fats to ketone bodies

carbohydrate metabolism

all food carbohydrates are transformed into glucose, which is further broken down into ATP via cellular respiration

lipid metabolism

triglycerides are broken down into glycerol and fatty acids, which are further converted into acetyl coA

protein metabolism

• amino acids are not stored for later use, they are oxidized or converted to fat

• amino acids are degraded into molecules that can be used by the citric acid cycle or that can be converted to glucose

glucose storage

• stored as glycogen if not needed for energy

  • in liver and skeletal muscles

  • when needed, can be broken down into glucose monomers via glycogenolysis

• when glucose is needed but not available, other nutrients can be converted via gluconeogenesis

lipid storage

• extra lipids are recombined via lipogenesis into triglycerides and stored

  • ends up in subcutaneous tissue or in fat deposits

  • when fat is needed, lipolysis occurs to release into blood

  • liver, cardiac muscle, and resting skeletal muscles burn fat as fuel

metabolic ketoacidosis

• when carbohydrate levels are low, lipolysis accelerates

• acetyl coA is produced and builds up, and the liver converts it into ketone bodies → accumulate in blood → ketosis → metabolic acidosis → blood pH drops and body cannot keep up → ketones are vaporized from lungs (fruity breath) → breathing rate increases → nervous system depresses → coma/death

total metabolic rate

• body’s rate of energy output

• influenced by

  • exercise

  • food ingestion - decreases after absorption

  • fasting - decrease in TMR to slow breakdown of body reserves

  • alcohol ingestion - increased metabolic activity of the liver

  • changing environmental conditions

basal metabolic rate

• amount of energy required for the performance of only the essential activities of the body

• influenced by

  • age - decreases with age

  • gender - generally higher in males

  • body temperature - increases during fever

  • stress - increases due to epinephrine and norepinephrine

more thyroxine =

increased oxygen consumption, heat production, and ATP use = higher BMR

body temperature regulation via

• radiation

• conduction

• convection

• evaporation

radiation

loss of heat in form of thermal energy

conduction

• transfer of heat via direct contact

• heat loss by touching and warming cooler objects

convection

transfer of heat via air circulation

evaporation

heat loss due to water eveporating

primary sex organs

• where gametes are produced

• testes produce sperm

• ovaries produce ova

temperature regulation in testes

• cremaster muscles - skeletal muscle bands that elevate testes

• dartos muscle - smooth muscle, wrinkles scrotal skin, pulls scrotum close to body

seminiferous tubules

site of sperm production

interstitial endocrine cells

produce testosterone

myoid cells

squeeze sperm out of testes

sustenocytes

nourish and support developing sperm

spermatogenic cells

sperm-forming cells

ovarian ligament

connects to uterus medially

broad ligament

continuous with peritoneum; includes uterus and fallopian tubes

suspensory ligament

connects laterally to pelvic wall

duct systems

• tubes that convey gametes to their destinations

• sperm travels from seminiferous tubules → straight tubule → rete testis → efferent ductule → epididymis (for storage until ejaculation) → ductus deferens → ejaculatory duct → urethra

• oocyte travels from ovary → uterine tubes [fimbrae → infundibulum → ampulla → isthmus] → uterus (implanted in wall if fertilized. if not, continues on) → cervix → vagina

accessory organs

organs or glands that produce secretions to aid in reproductive function

accessory to the testes

• seminal vesicles - produce seminal fluid, fructose

• prostate - secretes prostatic fluid, PSA

• bulbourethral glands - produce lubricating mucous to neutralize acidic urine in urethra

accessory to the ovaries

• bartholin glands - release lubricative fluid

• ducts - secrete fluid near vaginal orifice

• mammary glands - modified sweat glands with glandular alveoli that produce milk, which is passed into lactiferous ducts and into lactiferous sinus and then exits via the nipple

spermatogenesis

• produces 4 viable sperm

• mitosis of spermatogonia

  • spermatogonia divide → primary spermatocyte

• meiosis

  • primary spermatocyte (diploid) undergoes meiosis → secondary spermatocytes (haploid) → spermatids

• spermiogenesis

  • spermatids → sperm