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FOUNDATIONS IN HEALTHCARE > Digestion > Flashcards

Digestion Flashcards

1
Q

Describe the function of the digestive system

A

Is the breakdown of nutrients which can then be absorbed & used by cells to make ATP during cellular r/s & growth & repair

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2
Q

What is the alimentary canal?

A

A long muscular tube that extend from mouth to anus, also known as GI tract

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3
Q

What are the digestive organs and what are the accessory organs involved?

A

Digestive: mouth, pharynx, oesophaugus, stomach, small intestine & larger intestine
accessory: tongue, teeth, gallbladder,

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4
Q

Define mechanical & chemical digestion

A

Mechanical digestion: physical breakdown of food into smaller chunks e.g., teeth, creates larger SA for digestive enzymes, (small intestine segmentation & churning in the stomach)
Chemical digestion: refers to use of enzymes in breakdown of food e.g., lipase, pepsin

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5
Q

Describe the digestion pathway’s 5 stages

A
  1. Ingestion: taking in of food via the mouth into GI tract
  2. Propulsion: movement of food along GI tract, includes swallowing, peristalsis contractions & relaxations of muscle wall, squeezes food along
  3. Digestion: includes M & C digestion, ezymes secreted to breakdown food further, food is broken to chemical components
  4. Absorption: occurs in SI, nutrients absorbed via mucosal cells via active/passive transport. LI absorbs water & electrolytes
  5. Defecation: eliminates waste from the body as faeces via anus
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6
Q

Describe the components of salivia

A
  • 99% water
  • lipase enzymes
    -defensins
    -Amylase
    -Antibodies
  • Lysosomes
    -Good bacteria
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7
Q

What are the 4 layers found in the digestive system?

A

Serosa, muscularis, mucosa & submucosa

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8
Q

Describe the structure & function of the serosa

A

The outermost layer acts as a barrier, It anchors the GI tract in place.
It is made of squamous epithelium.
Involved in the protection & secretion of serum
Contains adventitia in oesophagus which binds it to surrounding structures

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9
Q

Describe the structure & function of the submucosa

A

It is external to the mucosa, a loose connective tissue which has lots of BV’s, lymphatic vessels & elastic fibres. EF allows stretch and shape recoil in stomach after digestion of a large meal. It secretes HCO3- to neutralize HCL, it contains the enteric NS

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10
Q

Describe the structure & function of the mucosa

A

The innermost layer that contains mucus membranes. This layer lines GI from mouth to anus, secreting enzymes, mucus & hormones. It absorbs end products in SI, it contains villi to increase SA for absorption. It contains lymphoid tissue to give protection & immunity

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11
Q

Describe the structure & function of the muscularis

A

The muscular layer in the GI tract. It is responsible for peristalsis & segmentation. It has an outer longitudinal layer & inner circular layer of smooth muscle cells.
Sphincters form along GI tract to control passage of food.
Extra layer found in stomach lining to aid in churning of food.

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12
Q

Define peristalsis

A

Peristalsis refers to involuntary wave-like contractions of the muscles in the digestive tract. These contractions help move food and other liquid particles through the digestive system to various processing organs. Peristaltic waves occur in the oesophagus, stomach, and intestines.

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13
Q

Describe the swallowing mechanism

A

Upper sphincter is contracted, tongue is pressed against the hard palate, forcing the bolus into the oropharynx

Pharyngeal-oesophageal phase begins, the tongue blocks the mouth, soft palate rises closing of nasopharynx, larynx rises so the epiglottis covers the trachea, upper sphincter relaxes, and food enters into the oesophagus

Muscles contract in the pharynx forcing food into the oesophagus, upper sphincter contracts again after food has entered

Peristalsis occurs moving food along to the stomach

GI sphincter opens, after food enters it closes to prevent regurgitation

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14
Q

What is the enteric NS?

A

GI tracts contains its own nervous system which staffs enteric neurons that communicate with each other about digestion activity.

Consists of nerve plexuses: submucosal & myenteric which run throughout GI tract & provide a major nerve supply & control GI motion
Submucosal found in submucosal layer
Myenteric found between muscular layers
It contains short & long reflex arcs: Short arcs are mediated by the enteric NS plexus in response to stimuli in GI
Long arcs use CNS integration & extrinisic autonomic nerves. Information is sent via the visceral sensory fibres. It recieves sympathetic & parasympathetic fibres from the ANS. These enter intestinal wall & to the plexus. Initiated by stimulation in & outside of the GI tract

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15
Q

Describe the enteric system pathway

A
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16
Q

Describe the structure & function of the oesophagus

A

is a muscular tube around 25cm long running through the mediastinum of the thorax, it transports food from the oropharynx to the stomach. Pierces through the diaphragm at the oesophageal hiatus to enter the abdomen. Joins to the stomach at the cardiac orifice.

Oesophagus has mucosa containing non-keratinized stratified squamous epithelial cells which changes to columnar cells in the stomach (needed for secretion). The submucosa contains mucus glands, as the bolus moves it compresses these glands causing secretion of mucus which greases the walls of the oesophagus allowing food bolus smooth passage.

It has a layer of smooth muscle (2/3) & skeletal muscle (1/3), involved in propulsion and peristalsis in the oesophagus. It also has fibrous adventitia (instead of serosa layer) which are made of connective tissue and coated in mucus to prevent friction in GI tract.

Passage of food occurs via flattening of mucosa folds, mucous glands & loose & elastic submucosa

17
Q

Describe the structure & function of the stomach

A

stores food and breaks it down mechanically & chemically, it can hold around 4L of food & water & extend to the pelvis. When stomach collapses mucosa & submucosa fold into rugae. The fundus is the dome-shaped top of the stomach covered by the diaphragm. The mid-portion of the stomach is referred to as the body, which continues down the pyloric part made of the pyloric canal & pyloric antrum.

Pyloric antrum narrows to form pyloric canal leading down to the pyloric sphincter which controls emptying of the stomach.

Stomach contains greater & lesser curvature which omentum extends from. Lesser omentum runs with continuous peritoneum which covers the stomach. The greater omentum covers the small intestine, has fat deposits & lymph nodes.

It has an extra layer of the muscularis which extends from the oblique muscle

Stomach secretes HCL, pepsin & mucus

18
Q

Describe the structure & function of the 4 cells types involved in the stomach lining

A

Mucus neck cells- produce a thin acidic layer of mucus different from other mucus cells

Parietal cells- found amongst chief cells, secrete HCL, have microvilli to provide a large SA for HCL secretion into stomach lumen. HCL provides acidic conditions needed for pepsin enzyme to digest proteins. Harsh enough to denature cell walls in plants & proteins as well as bacteria. HCL also controls harmful bacteria

Chief cells- found in basal regions of gastric gland, they produce pepsinogen which is the inactive form of pepsin. When stimulated pepsinogen is released & activated by HCL. Once pepsin is present it catalyses conversion of pepsinogen to pepsin, a positive feedback mechanism facilitated by levels of pepsinogen. It also secretes lipases which breakdown lipids.

G-cells (enteroendocrine cells)- release hormones into interstitial fluid e.g., histamine, which act as paracrine (activates different nearby cells), Gastrin hormone is secreted which regulates stomach secretion & motility

19
Q

Describe the steps involved in digestion of food in the stomach

A
  1. Propulsion: peristaltic waves move from the fundus to the pylorus (connects to duodenum)
  2. Grinding: most vigorous peristalsis waves towards pylorus. Pyloric end acts as a pump to deliver small amounts of chyme to duodenum
  3. Retropulsion: Peristaltic wave closes pyloric valve, forcing contents of pylorus back into the stomach
20
Q

Describe the structure & function of the small intestine

A

Has the 4 layers
Small intestine has circular folds which are deep permanent folds in the mucosa & submucosa which force chyme to spiral through to the lumen, slowing its movement giving more time for absorption.

Small intestine contains villi which are finger-like projections on the mucosa, they are large in the duodenum and gradually shorten & narrow throughout the small intestine. Each villus has a capillary bed & a lacteal (type of lymphatic vessel). Nutrients are absorbed into the capillary blood & the lacteal

Small intestine has microvilli which are long densely packed extensions on villi, they give mucosa a fuzzy appearance, they contain brush border enzymes on the border which complete carbohydrate and protein digestion

21
Q

Describe the structure & function of the duodenum

A

Duodenum contains the most features including duodenal papilla (where bile duct & pancreatic duct merge & empty their contents into the duodenum. It is a hollow c-shaped structure, 10 inches in length.

It contains the Brunner’s glands (duodenal glands) are tubuloalveolar, branched glands that open into the base of the crypts of Lieberkühn. Brunner’s glands manufacture a seromucous fluid rich in bicarbonates that acts to buffer the acidic chyme delivered from the stomach.

The duodenum allows the absorption of mineral & nutrients. Pyloric sphincter found between the duodenum and the stomach to control the passage of food. between the duodenum and the jejunum is the duodenojejunal flexure, which does not close and allows food to pass unobstructed.

Duodenum function: Cholecystokinin (CCK) is a hormone produced by I-cells in the lining of the duodenum.

It is released in response to the presence of proteins and fats to digest. CCK causes the increased production of hepatic bile, and stimulates the contraction of the gall bladder and the relaxation of the sphincter of Oddi, resulting in the delivery of bile into the duodenal part of the small intestine.

22
Q

Describe the structure & function of the jejenum

A

Jejunum extends from duodenum to the ileum, it is 2.5 metres long

Jejenum function:

Main Absorption of important nutrients such as sugars, fatty acids, and amino acids.

Vigorous and quick peristalsis to move nutrients through the digestive system.

Lined with longest villi to facilitate nutrient absorption.

Contains mucosal folds (rugue) to increase SA for absorption

Cleavage of nutrients by enzymes.

Absorption of lipophilic nutrients (proteins, fats, cholesterol, and fat-soluble vitamins).

Contains few brunners glands. PH ranges between neutral to alkaline

23
Q

Describe the structure & function of the ileum

A

The ileum is twisted & joins the large intestine at the ileocecal valve, it is 3.6m long

Ileum function:

Absorption of vitamin B 12 and conjugated bile salts.

Reabsorption of whatever products of digestion were not absorbed by the jejunum.

Secretion of protease and carbohydrate enzymes which help break down carbohydrates into simple sugars, and lipids into glycerol and fatty acids so they can be more easily absorbed by the body.

Release of certain digestive hormones, including cholecystokinin, gastrin, and secretin

Absorption of water and electrolytes.

Has lots of lymphatic tissue

24
Q

How does the small intestine receive blood?

A

The superior mesenteric artery supplies the small intestine with oxygenated blood, deoxygenated blood collected by the mesenteric veins drain back to the hepatic portal vein in the liver.

25
Q

Describe the function of Chyme

A

Chyme is an acidic fluid which passes from stomach to small intestine, consists of gastric juice & digested food. Functions:
- increase SA for digestive enzymes
- stimulate digestive glands to secrete e.g., CCK
- digest food, make liquid
- break food into smaller chunks

26
Q

Describe the structure & function of the cells involved in the small intestine

A

Paneth- found deep in crypts, secrete defensins & lysosomes, destroys bacteria & decides which bacteria to colonize the lumen
stem cells- found in depths of crypts dividing, differentiating & migrating up villi, paneth cells migrate down to the base of the crypt.
Goblet cells- mucus-secreting cell found in crypts
Enteroendocrine cells: source of CCK & secretin, main function is to release hormones when stimulated via digestive process, live in crypts & villi
enterocytes: form bulk of epithelium, simple columnar cells richly supplied with villi & tightly bound. Their main function is to absorb nutrients & electrolytes in the villi. Enterocytes found in crypts secrete intestinal juice (mix of watery mucus) that absorbs nutrients from the chyme. Enterocytes at tips of villi undergo apoptosis and are shed every 3-5 days

27
Q

Describe the structure & function of the intestinal crypts

A

Intestinal crypts: are tubular glands found between the villi, these crypts decrease in frequency along the small intestine, their function is Regeneration: They house stem cells that continually regenerate the intestinal epithelium as well as nutrient absorption: They aid in nutrient absorption. Also involved in protection: They protect against pathogens.

28
Q

Describe the mechanism of intestinal secretion

A
  1. CCK is secreted via duodenal enteroendocrine cells which is stimulated by fats & proteins in chyme
    secretin is released in the presence of acidic chyme, both S & CCK enter circulation
  2. CCK induces pancreatic secretion via the enzyme, S causes secretion of HCO3-, vagus nerve stimulates cephalic & gastric phases
  3. Bile is secreted via liver and stimulated via return of bile salts
  4. CCK causes gallbladder contractions, weak contractions caused by the vagus nerve
  5. Hepatopancreatic contraction occurs, CCK causes HP sphincter to relax, bile & Pancreatic juice enter the duodenum
29
Q

Describe the process of segmentation

A

Segmentation is a muscular activity that divides and mixes the chyme by alternating between backward and forward movement of the gastrointestinal tract (GI) contents. It is predominantly observed in the small intestine and large intestine of the GI tract. Segmentation is the process of mixing the food contents in the digestive tract to create a more uniform mixture throughout. It facilitates the continual division, fragmentation and blending of the material, helping food move slowly towards the end of the gastrointestinal tract while facilitating nutrient absorption through digestion.

30
Q

Describe the structure & function of the large intestine

A

Teniae coli- are 3 bands of smooth muscle, contain pocket structures called haustra.
Epiploic appendage fat filled pouched that hang from the large intestine, (signifcance not known)
The cecum is the first part of the large intestine, attached to the cecum is the appendix. The appendix contains lymphoid tissue so plays a role in immunity. Appendix stores bacteria and colonises gut bacteria when needed, appendix’s twisted structure makes it easy to become blocked.
- harvests vitamins and absorbs remaining water & electrolytes, main function of propulsion, force faeces down to the anus

31
Q

Describe the movement of faeces through the colon

A

Faeces move via haustral contractions, slow segmenting movements.
- pushes it to the sigmoid colon which stores it until it’s pushed into the rectum
- fibre strengthens haustral contractions and softens faeces

32
Q

Describe the structure & function of the anal canal

A
  • Has the standard 4-layer arrangement
  • it contains hemorrhoidal tissue that inflates to close the anus
  • rectal valves help hold the weight of faeces in the rectum
  • mucosa is the stratified squamous epithelium, different the rest of the colon to deal with abrasion
  • contains long ridges known as anal columns
  • anal sinuses found between columns which exude mucus when compressed, aids in canal emptying
33
Q

Describe the defecation mechanism

A
  1. faeces move into the rectum stimulating stretch receptors, this transmits signals along the spinal cord
  2. Spinal reflex is activated where PS motor fibres cause contraction of the rectum & sigmoid colon, during contraction, the glottis closes, and diaphragm & abdominal muscles contract to generate intra-abdominal pressure
  3. During contraction the levator ani muscle lifts up the anal canal, lifting action leaves faeces below the anus
  4. Anal sphincter relaxes, if suitable, the voluntary motor neurons are inhibited allowing external anal sphincter relax allowing faeces to leave the body
34
Q

Describe the functions of the gut microbiome

A

The gut microbiome consists of thousands of bacteria types, some colonize the colon
1. Fermentation: they ferment undigestible foods, making F.A’s to be absorbed via cells, produces 500ml of gas mixture daily
2. Vitamin B synthesis: B vitamins & K are synthesized in gut bacteria
K needed for haemostasias

35
Q

Describe how pathogenic bacteria are removed from the gut

A

They are removed in 2 ways:
1. the good bacteria out-compete the bad bacteria, suppresses them
2. dendritic cells sample foreign antigens and issue an immune response at lymphoid tissue, this restricts gut lumen, keeping the bacteria from travelling deep into mucosal tissue where more harm could be caused

36
Q

Describe the importance of the gut microbiome

A
  • it shapes our immune system, they work together to regulate inflammatory responses
  • gut has been linked to our mood, weight & likelihood to contract disease
37
Q

Describe the adaptation of the large intestine

A
  • no villi/folds as food is absorbed before reach LI
  • thicker mucosa
  • More & deeper intestinal crypts, loads of goblet cells, allowing easy passage
  • simple columnar epithelium cells

FOUNDATIONS IN HEALTHCARE (15 decks)

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