Bio topic 6

alimentary canal

organs through which food actually passes (oesophagus, stomach, small & large intestine)

accessory organs

aid in digestion but do not actually transfer food (salivary glands, pancreas, liver, gall bladder)

Stomach

A temporary storage tank where food is mixed by churning and protein digestion begins

It is lined by gastric pits that release digestive juices, which create an acidic environment

Pancreas

Produces a broad spectrum of enzymes that are released into the small intestine via the duodenum

Also secretes certain hormones (insulin, glucagon), which regulate blood sugar concentrations

Small Intestine

A long, highly folded tube where usable food substances (nutrients) are absorbed

Large intestine

Final section of alimentary canal, where water and dissolved minerals are absorbed

Consists of the ascending / transverse / descending / sigmoidal colon, as well as the rectum

Liver

Takes the raw materials absorbed by the small intestine and uses them to make key chemicals

Its role includes detoxification, storage, metabolism, bile production and haemoglobin breakdown

Peristalsis

the process of wave-like muscle contractions of the longitudinal muscles that moves food along

How does food move through the gut?

contraction of circular longitudinal musces of the small intestine

Chemical digestion : stomach acids

• Contain gastric glands which release digestive acids = low pH environment

• Acidic environment denatures proteins and other macromolecules

• Stomach epithelium = mucous membrane = prevents acids damaging gastric lining

• Pancreas releases alkaline compounds = neutralises the acids as they enter the intestine

Chemical digestion : bile

• Liver produces

• Stored and concentrated in gall bladder

• Released into the intestine

-Contains bile salts = emulsification of fat

• The emulsification of fats increases the total surface area available for enzyme activity (lipase)

Enzymes digest most...

macromolecules in food into monomers in the small intestine e.g. lipase breaks down fat

Digestion of Carbohydrates

• Begins in the mouth with the release of amylase from the salivary glands

• Amylase is also secreted by the pancreas in order to continue carbohydrate digestion within the small intestine

• Enzymes for disaccharide hydrolysis are often immobilised on the epithelial lining of the small intestine, near channel proteins

digestion of proteins

-Begins in the stomach with the release of proteases

• Smaller polypeptide chains enter the small intestine where they are broken down by endopeptidases released by the pancreas

• These endopeptidases work optimally in neutral environments as the pancreas neutralises the acids in the intestine

digestion of lipids

• Occurs in the intestines, beginning with emulsification of fat by bile

• The smaller fat droplets are digested by lipases released from the pancreas

digestion of nucleic acids

Pancreas releases nucleases = digest nucleic acids (DNA, RNA) into smaller nucleosides

What secretes enzymes into the lumen of the small intestine?

the pancreas

how many layers in the small intestine structure?

4

Serosa

protective outer layer

Muscle layer

outer layer of longitudinal muscle (peristalsis) and inner layer of circular muscle (segmentation)

Submucosa

connective tissue seperating the inner mucosa and the muscles

mucosa

a highly folded inner layer which absorbs through its surface epithelium

Villi

Fingerlike extensions of the intestinal mucosa that increase the surface area for absorption

Villi absorb

monomers formed by digestion and mineral ions and vitamins

Features of Villi

Mnemonic: MR SLIM

• Microvilli

• Rich blood supply

• Single layer epithelium

• Lacteals

• Intestinal glands

• Membrane proteins

Different types of membrane transport for digestion:

Endocytosis, Simple Diffusion, Osmosis, Facilitated Diffusion, Co-Transport/Active transport

Glucuoe and amino diffuse through...

co-transport

monosaccarides and hydrophillic diffuse through...

facilitated diffsuion

water diffuses through...

osmosis

hydrophopic substances transport through...

simple diffusion

Pinocytosis

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

Process of the digestion of starch in small intestine:

1. salivary amylase and pancreatic amylase are the enzymes which digest

2. Ammylose into maltose subunits

3. Amylopectin into dextrins

4. The hydrolysis of dextrins and maltose = production of glucose

5. This can be used to make ATP or stored as glycogen

6. The hormone insulin and glucagon regulate the concentration of glucose

Insulin

A hormone which lowers blood glucose levels

Glucagon

A protein hormone secreted by pancreatic endocrine cells that raises blood glucose levels

WIlliam Harvey discovered the blood system

were a combined network, blood flows continusouly, the heart is the pump (arteries from hear) (veins to heart), Blood flow is unidirectional

pulmoary circuit

on the right side of the heart

systemic circulation

on the left side of the heart

Arteries

Blood vessels that carry blood away from the heart

Characteristics of arteries

blood at high pressure, walls are thick, wales stretch or contract with a pulse, walls contain muscles cells and elastic fibres

Capillaries

Microscopic vessel through which exchanges take place between the blood and cells of the body

Characteristics of capllilaries

blood at low pressure, walls made of a single layer, extremly narrow lumen, facilatate material exhange

Cappliaries absorb

cell waste e.g. carbon dioxide and urea

Veins

Blood vessels that carry blood back to the heart

Characterisitc of veins

blood at low pressure, wide lumen, have valves, walls are thin, small amounts of muscles

Role of valves in the blood system

prevent backwards blood flow

heart structure

Pathway of deoxygenated blood through the heart

-Vena Cava (veins) from body

-Right Atrium

-Tricuspid valve

-Right Ventricle

-Pulmonary valve

-Pulmonary (artery)

-Lungs

Pathway of oxygenated blood

-from lungs

-Pulmonary veins

-Left Atrium

-bicuspid valve

-Left ventricle

-aortic semilunar valve

-aorta

-body

Sinotorial node

pacemaker on right atrium of heart

Describe the electrical events that trigger the contraction of the heart muscle fibres

• The heart beat is myogenic

• Electrical signals are initiated by the sinoatrial (SA) node

• It stimulates the atria to contract and also relays signals to an atrioventricular node

• The atrioventricular node sends signals via the Bundle of His to Purkinje fibres

• These fibres innervate the ventricles and cause them to contract

how is heart rate increased and decreased?

by impulses brought to the heart through two nerves from the medulla of the brain.

Describe the role of the medulla and epinephrine (adrenaline) in regulating heart rate

• The SA node maintains the heart's normal sinus rhythm (60 - 100 bpm)