Week 1 Flashcards by Molly Richard

Define digestion

Digestion is the chemical breakdown by enzymatic hydrolysis of complex foodstuffs to smaller, absorbable units.

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Define absorption

Absorption is the transfer of products of digestion from the digestive tract to the blood or the lymph

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What are the four layers of the digestive tract wall

Mucosa (inner layer)
Submucosa,
Muscularis Externa,
Serosa (outer layer)

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What effect does circular muscle and longitudinal muscle contraction have?

Contraction of circular muscle causes the lumen to become narrower and longer
Contraction of longitudinal muscle causes the intestine to become shorter and fatter.

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How are smooth muscle cells in the GI tract arranged?

The cells are arranged in sheets and coupled by gap junctions

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Explain the synchronous wave in smooth muscle

Spontaneous activity is triggered by pacememaker cells (modulated by nerves and hormones)
This activity causes slow waves which cause hundreds of cells contract at the same time

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What is meant by slow waves?

Rythmic membrane depolarisation and depolarisation that spreads from cell to cell via gap junctions

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What is the function of ICCs and where are they located?

These are the pacemaker cells which trigger electrical activity.
They are spread between the smooth muscle cells
(located between the longitudinal and circular muscle layers in the submucosa)

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In a smooth muscle cell action potential, what is the upstroke and downstroke mediated by?

The upstroke is mediated by voltage-activated calcium channels
The downstroke is mediated by voltage activated potassium channels

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What 3 stimuli affect whether slow wave amplitude reaches threshold?

Neuronal stimuli
Hormonal stimuli
Mechanical stimuli

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In terms of basic electrical rhythm, what is the frequency of slow waves in the; stomach, small intestine and large intestine?

Stomach - 3 per min 
Duodenum - 12 per min 
Ileum - 8 per min 
proximal colon - 8 per min
distal colon - 16 per min

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In the ENS system, what is the purpose of the myenteric plexus and the submucosa plexus

Myenteric plexus - Regulates motility and sphincters

Submucous plexus - Modulates epithelia and blood vessels

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Which is more important in terms of innervation of the G.I tract; parasympathetic or sympathetic?

PARASYMPATHETIC

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What effects do parasympathetic have on the G.I tract?

Increase secretions
Increase blood flow
Increase smooth muscle contraction
Relax sphincters and the stomach

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What effects do sympathetics have on the G.I tract?

Increase sphincter tone
Decrese motility
Decrease secretions
Decrease blood flow

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Where do parasympathetic and sympathetic fibres synapse?

PARASYMPATHETIC - Ganglion cells

SYMPATHETIC - Prevertebral ganglia

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What is peristalsis?

A wave of relaxation followed by contraction that proceeds along the gut in aboral direction

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What do circular and longitudinal muscles do in peristalsis?

Circular muscles contract

Longitudinal muscles relax

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What is segmentation?

The churning and mixing which is caused by contractions of the circular muscle layer

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How many sphincters are there in the G.I tract?

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Name the 6 sphincters in the G.I tract

Upper oesophageal 
Lower oesophageal 
Pyloric 
Ileocaecal valve 
Internal anal 
External anal

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Which two sphincters have skeletal muscle and are therefore usually under voluntary control?

Upper oesophageal sphincter

External anal sphincter

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What are the 3 major phases in swallowing?

Oral
Pharyngeal
Oesophageal

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What diseases can obesity contribute to?

T2DM 
Hypertension 
Osteoarthritis 
NAFLD (fatty liver disease) 
Dementia 
Stroke 
E.T.C

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What part of the brain is responsible for neural control of factors influencing energy intake and body weight?

HYPOTHALAMUS

What is CCK and when is it secreted?

Cholecystokinin | - Secreted in the duodenum and jejunum in proportion to meals

What is Ghrelin and when is it produced?

Grehlin is a hunger signal | Its level increase before eating and decrease after eating

What are the two hormones which inform the hypothalamus to alter energy balance?

LEPTIN and INSULIN

Outline the present drug therapy/management for obesity

``` ORLISTAT - Inhibits pancreatic lipase - Reduces fat absorption in the S.I BARIATRIC SURGERY - Gastric by-pass surgery - Restricts calorie intake - Substantial weight loss - Can resolve T2DM ```

Define glycogenesis and glycogenolysis

GLYCOGENESIS - Synthesis of glycogen to from glucose | GLYCOGENOLYSIS -Breakdown of glycogen to form glucose

What is gluconeogenesis?

GLUCONEOGENESIS - Generation of glucose from non-carbohydrate precursors

What is the primary source of glucose overnight?

Gluconeogenesis

What are the 4 enzymes involved in glycogenesis?

Hexokinase Phosphoglucomutase UDP-glucose pyrophosphorylase Glycogen synthase

What are the 3 enzymes involved in glycogenolysis?

Glycogen phosphorylase Phosphoglucomutase Glucose-6-phosphatase

What does Insulin do?

It stimulates glycogenesis by stimulating glycogen synthase | It inhibits glycogenolysis by inhibiting glycogen phosphorylase

What does glucagon do?

It stimulates glycogenolysis by stimulating glycogen phosphorylase It inhibits glycogenesis by inhibiting glycogen synthase

What are 3 of the main precursors for gluconeogenesis?

Lactate Amino Acids Glycerol

What is meant by a saturated or an unsaturated fatty acid?

Saturated have no double bonds Unsaturated have a double bond N.B polyunsaturated have multiple double bonds

What is lipolysis

The breakdown of stored fat to produce free fatty acids and glycerol Catalysed by lipases

What can high levels of ketone bodies cause?

Severe acidosis which impairs tissue function, particularly in the CNS

What is lipogenesis

Synthesis of lipids | Reductive process in which electrons are required

Where is the main site for amino acid degradation?

THE LIVER

What potentially toxic substance can amino acid breakdown release?

Ammonia and ammonium ions

What are the 3 steps in the synthesis of urea?

TRANSAMINATION DEAMINATION UREA CYCLE

What are the important points about the disease; phenylketonuria?

Degradation of phenylalanine is blocked, causing it to accumulate in all body fluids. Can cause severe mental problems. Can be controlled by an adequate diet.

What are the three major salivary glands?

PAROTID SUBMANDIBULAR SUBLINGUAL

Which part is the functional unit of a salivary gland and what does this part consist of?

The salivon - a secretory acinus - an intercalated duct - a striated duct

The composition of saliva varies according to flow rate. What happens to bicarbonate and potassium concentrations with altering rate?

Bicarbonate concentration increases as rate increases | Potassium concentration decreases as rate increases

Explain the unconditional and conditional reflexes involved in the control of salivary secretion

UNCONDITIONAL - simple - due to presence of food in the mouth CONDITIONAL - acquired - due to thinking/smelling food

What is the effect of parasympathetic and sympathetic stimulation on saliva production?

``` PARASYMPATHETIC causes ; Increased blood flow to the glands Increased fluid flow Increased contraction of myoepithelial cells SYMPATHETIC causes; decreased blood flow to the glands ``` both cause Increased secretion of a-amylase

What are the 5 gastric secretions of the oxyntic mucosa?

``` HCL Pepsinogen Intrinsic factor Histamine Mucus ```

What are the 3 gastric secretions of the pyloric gland area?

Gastrin Somatostatin Mucus

What is the function of gastrin?

Stimulates HCL secretion

What is the function of somatostatin?

Inhibit HCL secretion

What is the role of intrinsic factor?

It binds vitamin B12, allowing absorption in the terminal ileum

What are the three phases of gastric secretion?

Cephalic Gastric Intestinal

Name 4 classes of drugs that influence acid secretion

NSAIDs e.g aspirin Histamine receptor antagonists Proton-pump inhibitors Muscarinic receptor antagonists

What effect do prostaglandins have on the mucosa?

Reduce acid secretion Increase mucus and bicarbonate secretion Increase mucosal blood flow

Are ingested lipids soluble or insoluble?

Insoluble

How much of the daily energy requirement is provided by lipids?

55%

What substance emulsifies lipids? What is the purpose of this process?

Bile salts | - emulsifying large lipid droplets to small droplets increases their surface area for enzymatic hydrolysis

Which enzyme hydrolyses TAGs to monoglycerides and free fatty acids? (this is the main lipid digestive enzyme)

Pancreatic lipase

Which substance present in pancreatic juice neutralises stomach acid to provide a suitable pH for enzyme action?

HCO3-

Which hormone is released when there is fat present in the duodenum and what does secretion of this hormone cause?

CCK | - causes bile salts o be secreted in bile from the gall bladder

Where are bile salts synthesised and stored?

Synthesised in the liver and stored in the gall bladder

What kind of pH is required for the process of emulsification?

Neutral/ Slightly alkaline

What 2 adverse effects can occur if there is failure to secrete bile salts?

- Lipid malabsorption (steatorrhoea - fat in faeces) | - Vitamin deficiency due to failure to absorb lipid vitamins

What are micelles and where are they formed?

Small lipid particles - formed in the duodenum

What factor determines the fate of a fatty acid on entering a cell?

Its length

Which protein is involved in cholesterol absorption and transport?

NPC1L1

Which drug prevents the action of NPC1L1 for cholesterol absorption and can therefore be used for hypercholesterolaemia?

Ezetimibe

Which mode of transport is used in calcium absorption for low vs high concentrations of calcium in chyme?

Low concentrations - Active transport | High concentrations - Passive transport

What two substances regulate calcium absorption?

1,25-dihydroxyvitamin D3 (calcitriol) | Parathyroid hormone

Is Ferrous(Fe2+) or Ferric (Fe3+) the absorbable form of iron?

Ferrous (Fe2+)

What is the main storage form of iron within the cell?

Ferratin

What hormone is released from the liver when iron levels in the body are too high?

Hepcidin

What must all carbohydrates first be broken down into for digestion?

monosaccharides

What are the two main enzymes involved in the digestion of carbohydrates?

a-amylase | ogliosaccharidases

List some causes of lactose intolerance

- Lack of the 'lactate persistence allele' - Damage to the S.I e.g coeliacs disease/crohn's disease - Congenital

Signs and symptoms of lactose intolerance

``` Bloating Abdominal pain Flatulence Loose stools Diarrhoea ```

Which sodium-glucose transporter works in the small intestine?

SGLT1

Fructose, unlike galactose and glucose, is not a substrate for SGLT1, what is its alternative transport mechanism?

Fructose is transported by GLUT5

Which GLUT is responsible for EXIT of all monosaccharides from a cell? Across which membrane does this occur?

GLUT2 | - basolateral membrane

Which two substances must proteins be digested to for efficient absorption?

Oligopeptides | Amino acids

Which two substances are important for digestion in the stomach?

HCL (denatures proteins) | Pepsin (cleaves proteins in to peptides)

Which group of enzymes are important for digestion in the duodenum?

Pancreatic proteases

What is the difference between endopeptidases and exopeptidases?

ENDOpeptidase - cleave peptide bonds in the centre of the chains EXOpeptodase - split off amino acids from the ends of the chains

Amino acids exit enterocytes across the basolateral membrane by which transporters?

Na+ independent transporters

HCL is a gastric gland secretion, from which area of the gastric glands is it secreted and what is its function?

Secreted from parietal cells in the oxyntic mucosa. - It activates pepsinogen to pepsin - Denatures proteins and kills microorganisms

Enterochromaffin like cells are cells in the oxyntic mucosa of the gastric glands. What do these cells secrete?

Histamines | stimulates HCL secretion

Chief cells are cells within the oxyntic mucosa area of the gastric glands. What do these cells secrete?

Pepsinogen

Which two secretions come from the parietal cells in the oxyntic mucosa of the gastric glands?

HCL and Intrinsic factor

Which two cell types make up the pyloric gland area?

D cells and G cells

What is secreted from D cells in the pyloric gland area of the gastric glands and what is the function of this secretion?

Somatostatin | - Inhibits HCL secretion

What is secreted from G cells in the pyloric gland area of the gastric glands and what is the function of this secretion?

Gastrin | - Stimulates HCL secretion

a-amylase is an endoenzyme, meaning it can break down internal linkages but not terminal linkages. What are the products of carbohydrate digestion by a-amylase?

Linear glucose oligomers and a-limit dextrins

Ogliosacchardies cleave terminal linkages in carbohydrates to farm what product?

GLUCOSE

Pepsin is a protease enzyme (cleaves proteins into peptides). Is it an endopeptidase or an exopeptidase?

ENDOPEPTIDASE

Give an example of an endopeptidase enzyme and an example of an exopeptidase enzyme

ENDOpeptidase - trypsin | EXOpeptidase- procaroxypeptidase

How are oligopeptides transported across the apical membrane?

H+ oligopeptide co-transporter PepT1