Digestion

What’s the inner layer of the GIT?

mucosa

Name 2 types of mucosas and where they are found and why?

1. folded→ absorption / digestion
2. straight→ quick movement (oesophagus)

What’s over the mucosa?

Submucosa

What’s the enteric nervous system?

3rd division of nervous system

What’s in the submucosa?

Blood vessels + Nerves + Glands

What’s the function of the Meissner’s Plexus?

Determine vessels diamter/ secretions

→ control of submucos

What are the two layer of muscle ?

Inner= circular

Outer= longitutal

(inner part of the egg (zoltko) is a circular ball, outer is a long oval)

What’s the serosa?

smooth muscle layer

List the three phases of swallowing?

1. oral
2. pharyngeak (respiratory inhibited to prevent choking)
3. oesophageal

Where’s the swallowing centre?

Medulla

What receptors are in the pharynx?

Touch receptors

What are the 3 commands that the swallowing centre sends in the medulla?

1. soft palate blocks nasal and epiglottis and larynx blocks the trachea
2. upper oesophageal sphincter relaxes
3. peristakic wave

What cells line the oesophagus?

Squamous (flat cells)

What are the types of muscle that control the oesophagus?

1/3 skeletal

1/3 skeletal & smooth

1/3 smooth

Where’s the lower oesophageal spincter?

near the stomach to prevent reflux

In the stomach what does the mucosa contain?

Gastric glands that release gastric juices

What do goblet cell secrete?

mucus and HCO3-

(both protect the stomach from autodigestion)

What do pariental cells secrete?

HCl and intrinsic factor

What does intrinsic factor contain?

B12

Why is B12 needed?

To absorbe iron (pernicious anaemia)

What do enterochromaffin-like cells secrete?

Histamine and Serotonin

\

What does serotonin and histamine control?

Pancreas

What do chief cells secrete?

pepsinogen

What activates pepsinogen?

HCl

Name the 2 hormone secreting cells in the stomach?

G cells

D cells

What do G cells secrete?

Gastrin

What do D cells secrete?

Somatostatin

What are secretagogues?

They gauge out secretions (cause the secretion of an other substance)

What stimulates the release of HCl?

* histamine
* Acetylcholine
* gastrin

How does the stomach churn?

Peristaltic waves

How is the gastric slow wave regulated?

by the pacemaker zone in the fundus

What’s stronger fundus& body or antrum?

Antrum at the bottom because that’s where most food is

What’s the pylorus?

Sphincter acting

→ prevents chyme in the duodeum

What nerves cause the contriction of the pylorus?

Sympathetic and Vagus

What does the vagus do to the pylorus?

constrict and relax

How does the antrum work with the duodeum?

contracts as a unit “ atral systole”

duodeum relax

a few ml of chybe → duodeum

What are the three regions of the duodeum?

Duodeum/ Jejunum/ Illeum

What are the functions of the jejunum and illeum?

reserve , most work happens in the duodeum

What’s the brush border?

Microvilin

What are the brush border enzymes?

sucrase , aminopeptidases

Where is the pacemaker for the small intestine?

Near bile duct

What does the dile duct do?

Deliver liver and pancreatic secretions

Does motility get faster or slower as yoi go down in the small intestine?

Slower

What segmentation?

Mixes chyme with enzymes and mucous

What cells generate the contraction pace in the SI?

Interstitial cells of Cajal

What kind of waves are produced by the interstitial cells of Cajall

slow

(faster at the proximal end)

What’s the function of the large intestine?

Absorb salt and water

What’s the haustra?

Folded outer surface of the large intestine

Order

sigmoid colon/ transverse colon/ descending colon and rectum

Transverse

Descending

Sigmoid

Rectum

What’s the valsalva manoeuvre?

Expiring against a closed glottis which raises vein pressure

Is digestion regulated?

No, only secretions and motility is

What regulates the GIT?

Hormones and neural control

What cells produce gastric acid?

Pariental cells

Why is gastric acid needed?

Pepsinogen→ pepsin

How do pariental cells generate protons?

CO2+ H20

(carbonic anhydrase)

H2CO3→ H+ + HCO3-

What happens to the H+ generated by pariental cells?

Pumped outside the cell into the gland duct by active transport

What happens to Cl- in the pariental cells?

Pumped against conc. gradient in the cell

this allows HCO3- to get out

no overall change in charge!

What ion is taken in when the proton leaves the pariental cell?

(anion exchange H+ & ____)

K+

What cells secrete pepsin

Chief cells

What stimulates pepsin?

gastrin , acetylcholine and acid

What cells make the mucous?

Gastric neck cells

What cells secrete bicarbonate?

Epithelial cells

What are the three phases of gastric acid regulation?

Cephalic (brain)

Gastric

Intestinal

How is the cephalic phase initiated?

Smell taste→ tells pariental cells stimulated

What nerve controls the cephalic phase response?

Vagus

What initiates the stimulatory gastric phase?

Food in stomach

amino acids released

G Cells release gastrin→ gastrin stimulates pariental cells→ HCl released

→ chief cells release pepsinogen

How is the gastric phase regulated?

If pH falls below 2 = negative feedback and parinetl cells stop producing HCl

What type of response is the intestinal phase?

Inhibitory

What mediates the intestinl phase?

chyme in duodeum= imhibition of more acid released

What three things are released in the inhibitatory intestinal phase?

1. Secretin
2. Gastric Inhibitatory Peptin
3. Cholecytokin CCK (stops motility and secretion)

What are peptic ulcers

erosion of mucous membrane

What two nerve thingies make up the enteric nervous system?

Meissner’s Plexus = control of secretions (sounds german and they love when sauerkraut secretes acidic juices)

Auerbach/ myenteric = control of muscles layers

What nerves supply the enteric nervous system?

para/ sympathetic?

Para and sympathetic

How does the ENS control the pacemaker cells in the GIT?

They can speed it up/down

not activate (will work regardless of ENS status)

What’s the gastroileal reflex?

gastric activity= illeal motility

How is the gatroileal reflex protectory?

If intestine stretches (ouch) = stomach will slow down

How do paracrine secretions act?

Locally

Where do paracrine secretions get released from

intestinal/ gastric mucosa

What does motilin do?

Stimulate contraction of stomach antrum and duodeum

Where do exocrine glands secrete?

Into ducts

What are the 3 pairs of salivatory glands?

1. Parotid
2. Submandibular
3. Sublingual

What are the 2 cell types in salivatory glands?

1. Serous acinar cells
2. Mucous acinar cells

What do mucous acinar cells do?

secrete glycoproteins

What do glycoproteins do?

Make mucin

What do serous acinar cells do?

secrete water, ionrganic salts and amylase

Compare plasma and saliva ion levels?

lower Na+ and Cl-

\
higher K+ and HCO3-

What’s the pH of saliva?

6\.2

Is saliva hyper/ hypotonic?

Hypotonic

\
less ions than in plasma (plasma has more functions)

What is the first stage of saliva formation?

serous cells produce isotonic secretions

What does the isotonic secretion contain?

Amylase

What happens to the isotonic secretion?

Duct cells extract Na+ and Cl-

\
Add K+ and HCO3-

Which division of the nervous system controls the secretion?

Parasympathetic

\
(salivaring at icecream is very much not flight r fight)

But sometimes you have to fight for the icecream

* a little sympathetic

Is the pancreas endocrine or exocrine?

both!

endo= insulin (that travels!)

exo= enzymes into ducts

What are the two compoments of the pancreatic juices?

1. enzymes
2. bicarbonate (neutralises chyme)

What stimulates the secretion of enzymes from the pancreas?

Secretin and ACh

What produces the aqueous component of pancreatic juice?

Epithelial cells lining the duct

Is the aqueous compoment hypotonic?

Nope

Isotonic

however HCO3- levels are increased due to the need to neutralise

How is bicarbonate produced in the epithelial cell of the duct?

water and carbon dioxide move into the cell

bicarbonate is made

H+ fucks off into the plasma and therefore Na+enters

HCO3- goes to do its job in the duct and Cl- goes in the cell to neutralise

So how is the primary aqueous secretion modified?

water addded

Na+ and HCO3- added

What inactive enzymes do acinar cells release?

Trypsin

Chymotripsin

Carboxypeptidase