Physiology Flashcards
What are the main compartments of the digestive tract?
- Oral cavity
- Pharynx
- Oesophagus
- Stomach
- Small intestine
- Colon
- Rectum
What are accessory organs of the digestive tract?
- Tongue
- Teeth
- Salivary glands
- Pancreas
- Liver
- Gallbladder
Active process of food entering the oral cavity
What is the term for this?
Ingestion
Crushing, shearing and chewing of food
What is the term for this?
Mechanical digestion and propulsion
Chemical breakdown of food into small organic and inorganic molecules
What is the term for this?
Chemical digestion
Release of water, acids, enzymes, buffers and salt
What is the term for this?
Secretion
Movement of organic molecules, vitamins, electrolytes, minerals and water across digestive epithelium
What is the term for this?
Absorption
Elimination of waste products from body
What is the term for this?
Defecation
→ Caustic effects of digestive acids and enzymes
→ Mechanical stress
→ Bacteria
What do the above provide to the digestive tract?
Protection
What is the function of the oral cavity in digestion?
- Sensory analysis of food before swallowing
- Mechanical digestion (teeth, tongue, palatal surfaces)
- Lubrication → mixing food with saliva and mucus
- Limited chemical digestion of carbs and fats
How much saliva do the salivary glands produce daily and what does it consist of?
1-1.5l per day of saliva
→ 99.4% water, 0.6% electrolytes, buffer, glycoproteins, enzymes, antibodies, waste
→ Keeps oral surfaces clean
What is the function of the pharynx in digestion?
Muscular propulsion of bolus into oesophagus
What is the function of the oesophagus in digestion?
Actively moves swallowed food to stomach
How long is the oesophagus usually?
Approx. 25cm
What are the main characteristics of the stomach?
- Receives food from oesophagus → temporary storage
- Mechanical digestion → muscle contraction
- Chemical digestion → acids and enzymes
- Expendable tube-like organ
- Shaped like a “J”
Which organ is shaped like a J?
The stomach
Where does 90% of the nutrient absorption happen in the body?
Small intestine
How long is the small intestine usually?
Approx. 6 meters
What are the 3 segments of the small intestine?
Duodenum
Jejunum
Ileum
What are characteristics of the duodenum of the small intestine?
first 25cm → mixing bowl
What are characteristics of the jejunum of the small intestine?
2.5m → bulk of chemical digestion and nutrient absorption
What are characteristics of the ileum of the small intestine?
3.5m → controls flow of material to large intestine via ileocecal valve
What is the name of the valve between small and large intestine?
ileocecal valve
What are the 4 main layers of the small intestine?
Mucosa (Inner Layer)
Submucosa
Muscular layer
Serosa (outer layer)
What does the mucosa of the small intestine consist of?
→ Made of epithelium, areolar tissue and m. mucosae
→ Moistened by glandular secretions
What does the submucosa of the small intestine consist of?
→ Irregular CT
→ Between mucosa and muscular layer
→ Contains blood and lymphatic vessels and nerves
What does the muscular layer of the small intestine consist of?
→ Contains smooth muscle cells
→ Innervated by parasympathetic and sympathetic nervous system
What does the serosa of the small intestine made of?
→ Made of Collagen
→ Turns into peritoneum
What are the villi and where can they be found?
→ Finger-like projections inside of the small intestine
→ Increase surface area
- e.g. on the plicae
What are the plicae of the small intestine?
→ Folds in small intestines
What shape do the large intestine and rectum have?
Horseshoe shaped
What is the average length and width of the large intestine?
- Average length 1.5m
- Average width 7.5cm
What are the 3 main compartments of the large intestine?
→ Cecum: first portion (ileocecal valve💡)
→ Colon: largest portion
→ Rectum: last 15cm (Anus = exit of anal canal)
What is the main function of the large intestine?
→ Storage of digestive wastes
→ Reabsorption of water
What is the main function of the rectum?
→ Temporary storage of faeces
Where is the pancreas positioned and what does it look like?
- Dorsal to stomach
- Grey-pink colour
- 15cm long
- Release of digestive enzymes
What are the 2 main functions of the pancreas?
Endocrine:
→ Secretion of insulin and glucagon into blood stream
→ Controls blood sugar
Exocrine:
→ Secretion of pancreatic juice in small intestine
(juice is alkaline mixture of digestive enzymes, ions and water)
Where is the liver positioned and what does it look like?
- Sits in right hypochondriac and umbilical region
- Reddish-brown colour
- Approx. 1.5kg
- Approx. 100k lobules → functional units of the liver
- More than 200 different functions
Which organ has more than 200 different functions and approx. 100k lobules (functional subunits)?
the liver
How many lobes does the liver have?
2 (1 right -> bigger, 1 left -> smaller)
What are the 3 main functions of the liver?
Metabolic regulation
Hematolic regulation
Bile production
Which organ has the largest blood reservoir of the body?
The liver
Receives approx. 25% of cardiac output
Where is the gallbladder situated and what is its function?
- Sits in fossa dorsal to liver
- Hollow and pear shaped
- Storage of bile
- Modification of bile
What are the 2 main components of motility in the digestive tract?
Peristalsis and segmentation
What is peristalsis?
- Propulsion of bolus by one contraction after another
- Circular muscles
- Longitudinal muscles
- Continuous process
What is segmentation?
- Bolus fragments or entire bolus is mixed with intestinal secretions
- No set pattern
- Usually in small intestine, some in large intestine
What coordinates the activity of the digestive glands and the digestion process?
Local factors (e.g. in response to pH)
Hormonal mechanisms
Neural mechanisms
How long does the absorption in the small intestine usually take?
Approx. 5 hours from duodenum to ileum
What does the large intestine absorb?
- Reabsorption of water
→ 1,5l of food intake are reduced to 200ml of faeces - Absorption of bile salts, vitamins, organic waste and various toxins
What are carbohydrases?
Enzymes that break bonds between monosaccharides → Maltase, Sucrase, Lactase
During digestion
What are proteases?
Enzymes that break bonds between amino acids
What are lipases?
Enzymes that break bonds between fatty acids (glycerides)
- Decrease in division rate of epithelial stem cells
- Decrease in smooth muscle tone
- Cumulative damage effects become apparent
- Increase in cancer rates
- Dehydration is common
- Direct or indirect influence on digestive system due to changes in other systems
What are these effects?
Effects of ageing on digestion
What are the two main states of metabolic activity in digestion?
Absorptive state
Postabsorptive state
When does the absorptive state of digestion start and how long does it last?
- Starts immediately after meal
- Lasts up to 4 hours
Which hormone is the primary hormone in the absorptive state of digestion?
Insulin
For which purposes do cells absorb nutrients in the absorptive state of digestion?
→ Growth
→ Maintenance
→ Energy reserves
What is the postabsorptive state of digestion and how long does it last?
- Time between meals
- Lasts up to 12 hours
- Period when body has to rely on absorbed nutrients
Which hormones are highly active in the postabsorptive state of digestion?
glucagon
glucocorticoids
adrenaline
GH
What do liver cells ensure during the postabsorptive state of digestion?
→ Transport of energy reserves
→ Maintenance of blood glucose levels
When do ketone bodies form in the postabsroptive state of digestion?
If carb reserves have been fully depleted
What is a normal pH value in the body?
7.35 - 7.45
What is the pH value when there is acidosis?
< 7.35
What is the pH value when there is alkalosis or basis?
> 7.45
What happens if the pH drops between 6-7?
death
What happens if the pH rises between 7.8-9?
death
What happens in the body if the pH is out of the normal zone?
- Deterioration of CNS → potentially leading to coma
- Cardiac contractions grow weak and irregular
- Peripheral vasodilation produces decrease in BP and circulatory collapse
What are fixed acids?
→ Once produced they remain in body fluids until eliminated in kidneys
→ Sulphuric acid, phosphoric acid
What are organic acids?
→ By-products of metabolism
→ Lactic acid or ketone bodies
What are volatile acids?
→ Can leave body by entering air through lungs
→ Carbonic acid H2CO3
What does net loss of body minerals in elderly cause?
Decrease in muscle and skeletal mass
What does a decrease in ability to concentrate urine cause in elderly?
Strong increase in H2O loss via urine
What does a decrease in glomerular filtration and functional nephrons cause in elderly?
Decrease in ability to regulate pH
What does a decrease in vital capacity cause in elderly?
Respiratory acidosis
What is the water content of the body at birth?
Approx. 75%
What is the water content of the body in elderly?
Approx. 55% in male, 47% in female