Bioveterinary Sciences & Biological Sciences Notes - Integrated Physiology II

Bioveterinary Sciences &
Biological Sciences Notes
Royal Veterinary College, D300

INTEGRATED PHYSIOLOGY II
Gastrointestinal Tract ............................................................................................................... 1
Introduction and Overview of the Alimentary System ................................................................... 1
Histology of the Alimentary System ............................................................................................... 6
Gut Secretion and Motility............................................................................................................ 13
Digestion and Absorption ............................................................................................................. 21
Comparative Physiology ............................................................................................................... 28
Intermediary Metabolism ....................................................................................................... 33
Introduction to the Intermediary Metabolism ............................................................................. 33
Anaerobic Metabolism.................................................................................................................. 37
Aerobic Metabolism...................................................................................................................... 41
Fatty Liver ..................................................................................................................................... 46
Integration of Metabolism Pathways ........................................................................................... 57
Nervous System ..................................................................................................................... 62
Autonomic Nervous System.......................................................................................................... 62
Special Sense Organs .................................................................................................................... 74
Cardiovascular and Respiratory System (CVRS)........................................................................ 81
Organisation of the CVRS ............................................................................................................. 81
Functional Anatomy of the Respiratory System ........................................................................... 91
Regulation of Cardiac Output ....................................................................................................... 98
Regulation of Heartbeat ............................................................................................................. 112
Reflex Control of the Circulation ................................................................................................ 125
Ventilation and Perfusion ........................................................................................................... 132
Ventilation and Perfusion Relationships..................................................................................... 140
Regulation and Control of the Respiratory System .................................................................... 150
Renal System ....................................................................................................................... 157
Introduction to Renal Physiology ................................................................................................ 157
Tubular Function and Water Balance ......................................................................................... 165
Role of the Kidney in Body Fluid Homeostasis – Calcium and Phosphate .................................. 172
Renal Distal Tubular Function and Body Fluid Homeostasis – Sodium and Acid-Base ............... 175

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Introduction and Overview of the Alimentary System
 Appreciate the overall layout of the gastro-intestinal tract from headgut,
through foregut and midgut, to hindgut, including associated glands, with an
understanding of major functions along the GIT.

 Describe the cellular arrangement of the GIT, highlighting the common patterns
and variations along its length, explaining how these relate to regional
function.



The purpose of digestion is to supply the organism with nutrients and materials required for ATP
production. Digestion includes the processes of:

1. Ingestion into the body
2. Reduction into smaller particles
3. Absorption into the bloodstream/circulation
4. Elimination of waste products


Headgut: Lips, tongue, mouth, and teeth
- Ingestion takes place here
- Beginning of reduction through prehension (getting food in mouth) and mastication (chewing)
- Saliva produced by salivary glands + release of digestive enzymes (e.g. amylase)

Foregut: from distal oesophagus down to proximal half of 2nd part of the duodenum
- Stomach, liver, gallbladder and bile ducts, pancreas (dorsal and ventral)
- A lot of mechanical and chemical breakdown to increase surface area for enzymes
- Numerous digestive enzymes secreted

Midgut: distal half of 2nd part of duodenum down to proximal 2/3 of the transverse colon
- Cecum, appendix, ascending colon, proximal 2/3 of the transverse colon
- The first part of the small intestine is largely associated with the breakdown
- Latter parts of the intestine are involved in absorption
- Shape: fundus (top of the stomach), body (central region), pylorus (hind part of the stomach),
sphincters (at the end of oesophagus and entrance of the duodenum)
- Muscular walls for contraction and rugae (a series of ridges produced by folding of the wall of
an organ – allows for expansion of the stomach after the consumption of food/liquid)
- Gastric pits (HCl secretion) – lowers pH (important for enzyme activation + defence
mechanism against pathogens)

Hindgut: distal 1/3 of transverse colon to the rectum
- Rectum, upper anal canal, urogenital sinus
- Small intestine: duodenum (relatively short), jejunum (relatively long), ileum (absorption)
- Mucous secretion (acid protection) and fluid (normally alkaline to neutralise the acid)
- Water and electrolyte reabsorption to maintain osmotic homeostasis

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Uptake of nutrients and absorption can take place via:
 Simple diffusion – through the phospholipid bilayer down the concentration gradient
 Facilitated diffusion – involves a carrier protein built into the bilayer (also down the conc. gr.)
 Active transport – involves a carrier protein and requires ATP. Against the conc. gr.
 Co-transport – two types of molecules and carrier proteins involved + ATP needed
 Endocytosis – budding off of the bilayer and internalising the product in a vesicle




Liver – the function of hepatocytes
The nutrient-rich blood from the gut first passes through the liver before entering the circulation to
the rest of the body.

 Synthesis of bile – a detergent that helps to break down fat into small particles and increase
surface area for lipases.
o Bile is stored and concentrated in the gallbladder, followed by secretion into the
duodenum
 Metabolism – fat breakdown to produce energy (as well as carbohydrates and proteins)
 Storage – excess glucose stored in a form of glycogen in the liver
 Biotransformation – amino acids to proteins and breakdown of toxins in the diet
(detoxication)
 Synthesis of blood component – e.g. clotting factors, red blood cell filtration to excrete waste
from erythrocyte recycling


Pancreas
Secretes pancreatic juice into duodenum at duodenal papilla.

The pancreas has an endocrine function because it releases juices directly into the bloodstream, and
it has an exocrine function because it releases juices into the duodenum.

Pancreas also produces insulin and secretes it into the bloodstream, where it regulates the body’s
glucose concentration.

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Small intestine – nutrient absorption (small diameter)


Duodenum Chemical digestion


Jejunum Nutrient absorption

Absorption of vitamin B12,
bile salts, and any products
Ileum
of digestion that were not
absorbed by the jejunum


Large intestine (colon) – water + electrolyte absorption (large diameter)

Caecum
Midgut
Ascending colon

Transverse colon Midgut/Hindgut

Descending colon
Hindgut
Rectum


Water and electrolyte absorption
The large intestine is mainly associated with water and electrolyte (Na+, Cl-, K+) absorption.
Bicarbonate is also present in the colon and its function is to neutralise the stomach acid.




KIDNEY
DIAPHRAGM




LIVER



DOG

, 4




Control of the gastro-intestinal tract
Endocrine (slower response, more energetically favourable)
Hormones are released into the circulation by cells within the Git or an accessory organ. Example:
gastrin increases gastric acid secretion.

Paracrine (slower response, more energetically favourable)
Mediators are released by cells within the tract and diffuse locally to act on neighbouring target cells.

Nervous (fast, energetically costly)
 Intrinsic control from the enteric nervous system – submucosal plexus (control of submucosal
glands) and myenteric plexus (control of contractility of the muscles)
 Extrinsic control from the central nervous system – autonomic nervous system (sympathetic
and parasympathetic)

, 5


Pancreas structure




Stomach structure

, 6



Histology of the Alimentary System
 Explain the basic layout of the layers of the GIT, and highlighting appropriate
regional variations that reflect local functional adaptations.

 Discuss species-specific variation in the arrangement of the GIT, reflecting diet
and anatomy.


Example of
Type Diagram Functionality
where found

Small intestine /
Simple Secretion, absorption, ciliated tissues in
columnar and protection bronchi and
uterus


Ovaries / in ducts
Simple Secretion and and secretory
cuboidal absorption portions of small
glands


Allows materials to Bowman’s
Simple
pass through by capsule/air sacs
squamous
diffusion and filtration of the lungs




Stratified Protection and Ocular
columnar secretion conjunctiva


Lining large ducts
Stratified from sweat,
Protective tissue
cuboidal mammary and
salivary glands

Lines the
Stratified Protection against oesophagus,
squamous abrasion mouth, and
vagina

Impermeable and
Lines the bladder,
distendable. Allows
Transitional urethra, and the
the urinary organs to
ureters
expand and stretch

, 7


Simple – just one layer of cells, tends to have a secretory function
Stratified – multiple layers, tends to have a protective function

The nucleus isn’t always round, for example in simple columnar cells it tends to be long and thin.

Hollow organs of the gastrointestinal tract, such as the oesophagus, are lined by the epithelium of
endodermal origin. Type of epithelium varies in different regions of the tract and between species, in
accordance with their diet. The muscular layers of the gastrointestinal tract are derived from the
mesoderm.

There are four layers of the gut wall:

1. Mucosa (innermost)
a. Epithelium
b. Lamina propria
c. Lamina muscularis

2. Submucosa

3. Tunica muscularis

4. Basement membrane




GOBLET
CELL
COLUMNAR
SIMPLE
COLUMNAR
SIMPLE




LYMPHOCYTES




CANINE STOMACH SMALL INTESTINE

, 8




OESOPHAGUS
(CROSS SECTION)




SMALL
SUBMUCOSA
INTESTINE

, 9




EPITHELIUM




STOMACH
(FUNDUS)




STOMACH
(FUNDUS)