Digestive System and Reproduction

EXAM IV AP II Lec

functions of digestive system (mechanical and chemical)

•Break down food into nutrients

• mechanical digestion = physical breakdown of food into smaller pieces

• chemical digestion = breakdown of food by enzymes into nutrients

• Absorb nutrients into the blood for use by cells of the body

 Eliminate wastes

ingestion vs propulsion

•Ingestion

• mastication into a bolus

• Propulsion

• deglutition

• peristalsis

mixing in stomach (chyme), secretion of enzymes and absorption from lumen of _____ through intestinal epithelium into blood, egestion

•from the lumen of the intestines, through the intestinal epithelium, into the blood

order of digestive system

mouth, esophagus, stomach, small intestine, large intestine

teeth uses mechanical digestion to form bolus so salivary glands secrete ______breaks down carbs and mucins acts as _________

secrete salivary amylase and mucins act as lubricants/buffers

smooth muscle contractions (mechanical digestion), food remains in the stomach for _______ hours and no nutrients absorbed from stomach

3-4 hours

secrete enzymes for chemical digestion forming chyme (gastric glands in gastric pits)

•parietal cells – produce:

• HCl – reduces pH to 1.5-2

• intrinsic factor – for the absorption of Vit. B12

 chief cells – produce pepsinogen, which is converted to pepsin by acidic conditions.  Pepsin denatures proteins

pyloric glands have G cells gastrin and D cells somatostatin 

•G cells – produce gastrin, which stimulates parietal and chief cells, and stomach contractions (mixing)

• D cells – produce somatostatin, which inhibits gastrin release when food is not present

cephalic (stimulate senses of food), gastric and intestinal phase do what?

•cephalic phase – medulla oblongata stimulated by sight, smell, taste, or thought of food.  Parasympathetic system is activated; parietal, chief and G cells are stimulated.

• gastric phase –stomach distention stimulates enteric reflexes (mixing); continued secretion of gastric enzymes

• intestinal phase – duodenal secretions inhibit gastric glands

chyme leaves the stomach through pyloric sphincter and enters

duodenum

pancreatic juice and bile (from liver) enter duodenum through 

duodenal ampulla, mucins and lubricants protect cells from acidic chyme, buffers raise pH to 7-8

plicae

circular folds

villi

cellular extensions

microvilli

smaller cellular extensions

brush border

formed by microvilli

duodenum goblet, paneth and absorptive cells 

•goblet cells – secrete mucus

• Paneth’s cells – lymphatic tissue

• absorptive cells – produce brush border enzymes

duodenal cell types enteroendocrine cells (s, K, Brunners glands, i)

• S cells – in Crypts of Lieberkuhn, produce secretin (stimulates bile from liver and insulin from beta cells of pancreas)

• K cells – produce  gastric inhibitory polypeptide (inhibits gastrin and stimulates insulin)

• Brunners Glands – produce mucus and urogastrone (inhibits all gastric glands)

• I cells – produce cholecystokinin (stimulates pancreatic juice from acini)

•most absorption of nutrients (lots of plicae for greater absorptive area)

jejunum

ileum has gradual smoothing out of plicae and peyer’s patches

•Peyer’s patches – clusters of lymphatic tissue to protect against bacteria from the large intestine

large intestine has cecum and vermiform appendix, what are large intestine functions (absorption and compaction)

•water and vitamin absorption

• compaction and storage of feces

vermiform appendix

development of immunity and maintenance of gut flora

ascending colon then which?

transverse colon

after descending colon sigmoid colon and 

rectum/anus 

large intestine has haustra - pouches for expansion where diverticulitis is inflammation of haustra and cells that secrete mucus

goblet cells

mucosa histology (epithelium, lamina propria, muscularis mucosae)

•Epithelium – simple columnar (intestines and stomach), stratified squamous (mouth, esophagus, oropharynx, anal canal)

• Lamina propria – underlying connective tissue (contains blood vessels/lymphatic vessels and nerves)

• Muscularis mucosae – circular/longitudinal layers of smooth muscle

Submucosa

• thick layer of connective tissue with nerves, blood vessels, and lymphatic vessels 

submucosal plexus network of these two systems and _____ nerve fibers

• submucosal plexus – network of sympathetic, parasympathetic, and enteric nerve fibers

layers of smooth muscle (circular/longitudinal), extra oblique muscle layer in stomach called?

muscularis externa

muscularis externa has myenteric plexus

myenteric plexus – sympathetic, parasympathetic, and enteric nerves that control the muscular layers

serosa/adventitia is the _____ membranous layer

outermost

describe placement of serosa and adventitia 

•serosa – below the diaphragm; visceral peritoneum

• adventitia – above the diaphragm, connects esophagus to trachea and aorta

oxygen rich nutrient poor

hepatic artery

liver blood flow

-mixed blood

•nutrient-rich, oxygen-poor blood enters via hepatic portal vein

• oxygen-rich, nutrient-poor blood enters via the hepatic artery

• both sources of blood mix in the hepatic sinusoids, then leaves liver via hepatic veins

hepatocytes 

• produce bile from bilirubin (excess is stored in the gall bladder

• storage of glycogen, fat, vitamins

hepatocytes nutrient introconversion

•glycogenesis

•glycogenolysis

•gluconeogenesis

• deamination/transamination

• production of plasma proteins

• detoxification

kupffer cells in liver do phagocytosis and storage of

heavy metals like Iron

damage to hepatocytes, can be viral (hepatitis) or alcohol related

cirrhosis of the liver

symptoms of cirrhosis

symptoms:

-jaundice (too much bilirubin)

- ascites (fluid accumulation between visceral and parietal peritoneum from hypertension in hepatic portal vein)

- edema (peripheral swelling due to decreased production of plasma proteins leading to decreased BCOP…more filtration into tissues)

•Kupffer cells hoard iron

• symptoms: same as cirrhosis but high plasma Fe⁺⁺ also damages other organs

hemochromatosis

pancreas (proteases, pancreatic amylase lipases, deoxyribonucleases and ribonucleases)

Pancreas:

• Acini are stimulated by cholecystokinin and the parasympathetic system to produce pancreatic juice, which contains:

• proteases (trypsin, chymotrypsin, elastase)

• pancreatic amylase

• lipases

• deoxyribonucleases and ribonucleases

autoregulation stretch, pH, paracrine factors stimulate _____ of glands and these cells

•stretch, pH, paracrine factors stimulate secretion/inhibition of glands/cells (enteroendocrine cells)

nervous regulation involves (sensory receptors from enteric division of short reflexes and stimulation/inhibition of digestive activity from these two systems 

•parasympathetic – stimulates digestive activity

• sympathetic – inhibits digestive activity

• enteric division (short reflexes)

• sensory receptors directly stimulate enteric motor neurons in the submucosal and myenteric plexuses to activate peristalsis

¡Carbohydrate breakdown/absorption

 salivary amylase and pancreatic amylase break carbohydrates into

diasaccharides and trisaccharides

Brush border enzymes break disaccharides and trisaccharide’s into

monosaccharides

monosaccharides from brush border enzymes

¡ lactase – breaks lactose into  glucose and galactose

¡ maltase – breaks maltose into two glucose

¡ sucrase – breaks sucrose into glucose and fructose

absorbed into intestinal epithelium by facilitated diffusion through uniporters 

Monosaccharides are absorbed into intestinal epithelium by facilitated diffusion (through uniporters) and cotransport with Na⁺, then absorbed into the blood by diffusion

Protein breakdown and absorption

Proteases break down proteins into

dipeptides, tripeptides and amino acids

Absorption into intestinal epithelium using cotransport with Na+, then active transport into blood, how to get into intestinal epithelium??

proteins can be cotransported with H+ in combination with countertransport with K+, or just countertranported with H+ - all of these are multiporters

Lipid breakdown and absorption

Lipases break lipids into

fatty acids and monoglycerides 

micelles form

bile salts bind with monoglycerides and fatty acids

absorbed by simple diffusion into intestinal epithelium

micelles

Inside the cell, micelles are reconverted into triglycerides and coated with proteins to form

chylomicrons a type of lipoprotein

chylomicrons are exocytosed into ___ then return to blood 

lacteals 

Other types of lipoproteins (cholesterols):

LDL – 75% lipid (bad cholesterol), transports lipids from liver to cells, so HDL is ________

HDL – 55% lipid (good cholesterol), transports excess lipids from cells to liver

absorption of other nutrients

Water – moves osmotically

Ions – move according to concentration gradients

Calcium – actively tranported, depends on hormones (calcitriol, PTH, calcitonin)

Vitamins – fat soluble vitamins (A, D, E, K) are absorbed with micelles

                  - water soluble vitamins (B, C) use simple diffusion (except B12, which binds to intrinsic factor

Lipids supply energy at a slower rate than glucose, although more ATP per carbon

will be formed from a fatty acid then glucose molecule 

lipid uptake from blood is increased

Muscles use more lipids for energy during rest, and during endurance activities like weight-lifting

glucose uptake from blood is increased

They use more glucose for energy during intense activity

involves breaking an amino group off of one amino acid and attaching it to another keto acid

transamination - amino acids converted into other amino acids 

Some amino acids (ketogenic amino acids) are broken down in a process called deamination

where an amino group and a hydrogen are removed to form ammonia (toxic byproduct) and a keto acid

2.The keto acid reacts with coenzyme A to form acetyl coA, which enters the Kreb’s cycle.

Other amino acids (glucogenic amino acids) can be broken down directly into _____ acid

can be broken down directly into pyruvic acid, which also reacts with coenzyme A to form acetyl coA, which enters the Kreb’s cycle

is it better to use proteins for energy??

NO 1.) they are required for structural purposes, b) deamination results in toxic byproducts (ammonia), and c) deamination may also result in ketoacidosis.

testes contain this where spermatogenesis occurs

seminiferous tubules

located outside of body, require low temp for development, develop retroperitonelly and descend through inguinal canal before birth

testes

failure of testes to descend

cryptorchidism

Spermatogonia

stem cells on outer portions of tubule divide by mitosis into primary and secondary spermatocytes and spermatids

closer to the lumen, have 46
chromosomes, divide by Meiosis I into secondary spermatocytes

Primary spermatocytes

have only 23 chromosomes,
moving closer to the lumen, divide by Meiosis II into spermatids

secondary spermatocytes

at lumen, haploid, mature into spermatocytes 

spermatids 

Sustentacular cells

in seminiferous tubules; assist in spermatogenesis

blood testes barrier

maintains an environment conducive to sperm development

Secrete androgen-binding protein

increase T levels 

secrete inhibin’s

when stimulated by FSH; inhibits FSH production

seminal vesicles

produce fructose, prostaglandins, and fibrinogen

produces seminal plasmin (antibiotic)

prostate gland 

produces lubricants and buffers

bulbourethral cowper’s glands

GnRH

from hypothalamus, stimulates release of FSH and LH

FSH

stimulates sustentacular cells to promote spermatogenesis

LH

stimulates interstitial cells to produce testosterone

Testosterone

primary male androgen, stimulates sustentacular cells, protein/cartilage/muscle synthesis, secondary sex characteristics, sex drive

Oogonia in primordial follicles complete

mitosis before birth to create primary oocytes (in primary follicles)

Primary follicles pause

in prophase of Meiosis I

Each month after puberty, several primary oocytes complete Meiosis I and begin Meiosis II why??

to form secondary oocytes in secondary follicles)

Cytoplasm is unevenly distributed during meiosis, forming a

haploid ovum and polar bodies

ova do not complete Meiosis II

until fertilization

female GnRH – from hypothalamus, stimulates release of FSH and LH

GnRH levels fluctuate in response to estrogens (increase GnRH) and progestins (decrease GnRH) from the ovaries

female FSH stimulates

follicel development 

female LH

stimulates ovulation and formation of the corpus luteum

female progestins secreted by corpus luteum

decreases GnRH (and so FSH and LH)

hormones from ovarian cycle drive what?

uterine cycle 

female Estrogens (estradiol) – produced by follicles increases these 3 hormones

, increase GnRH (and so FSH and LH)

ovarian cycle

follicular and luteal 

uterine cycle 

proliferative, secretory and menses 

Shedding of endometrial lining due to lack of progestins and estrogens

menses phase uterine cycle

Endometrial glands secrete mucus due to progestins from corpus luteum

secretory phase uterine cycle

Buildup of endometrial lining due to estrogens from follicle and progestins from corpus luteum

proliferative phase uterine cycle

1.Primary follicles (pausing in prophase of Meiosis I) are stimulated by FSH – cells enlarge to create granulosa cells (zona pellucida) which produce estrogens with thecal cells surrounding follicle

follicular phase ovarian cycle

1.Secondary follicles – some primary follicles develop and produce follicular fluid

ovarian cycle follicular phase

1.Tertiary follicle – LH stimulates the completeion of Meiosis I (produce secondary oocyte and polar body) and the beginning of Meiosis II

ovarian cycle follicular phase 3

1.Ovulation – stimulated by GnRH and LH

last step of follicular phase ovarian cycle 

Corpus luteum – driven by LH – granulosa cells close off burst tertiary follicle.  Secretes progestins (which inhibit GnRH)

first step of luteal phase ovarian cycle