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NURX1003 > The Digestive System > Flashcards

The Digestive System Flashcards

1
Q

What is the digestive system ?

A
  1. The breakdown of larger food molecules into smaller molecules is called digestion
  2. The organs that collectively perform digestion and absorption constitute the digestive system
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2
Q

Functions - stages

A
  1. Ingestion – taking food into the mouth
  2. Secretion – release of water, acid, buffers and enzymes into the lumen of the GI tract
  3. Mixing and propulsion – churning and pushing food through the GI tract
  4. Digestion – mechanical and chemical breakdown of food
  5. Absorption – passage of digested products from the GI tract into the blood and lymph
  6. Defecation – elimination of feces from the GI tract
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3
Q

Alimentary canal

A
  1. Mouth
  2. Pharynx
  3. Oesophagus
  4. Stomach
  5. Small intestine
  6. Large intestine
  7. Rectum
  8. Anal Canal
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4
Q

Accessory organs

A
  1. Teeth
  2. Tongue
  3. Gall bladder
  4. Digestive glands
  5. 3 pairs of salivary glands
  6. The pancreas
  7. The liver
  8. Biliary tract
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5
Q

Concepts

A
  1. The digestive system controls the environment within its lumen to ensure optimal conditions for digestion and absorption of foodstuffs
  2. Receptors and hormone secreting cells in the GI canal wall respond to stretch and chemical signals that result in stimulation or inhibition of GI secretary activity or motility, the GI tract has a local nerve supply
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6
Q

Layers of the GI tract and the omentum

A
  1. Inside to the outside - The mucosa, submucosa, serosa
  2. Parts of the peritoneum – mesentery and greater omentum
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7
Q

GI tract structure and function

A
  1. The mucosa – innermost layer, moist epithelial layer, secretion of mucus, hormones and digestive enzymes, and absorption of the end products
  2. Digestion into blood
  3. Protection against infectious disease
  4. The submucosa – external to the mucosa, is rich in lymph and blood vessels, maintains shape
  5. The muscularis externa – responsible for segmentation and peristalsis, mixes and propels food
  6. Circular layer forms sphincters which act as valves to prevent back flow
  7. Longitudinal layer is the outer smooth muscular layer
  8. The serosa – protective outermost layer
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8
Q

Enteric nerve supply

A
  1. The GI tract has its own enteric neurons
  2. The submucosa nerve plexus - Regulates the glands and smooth muscle In the mucosa tunic
  3. The large myenteric nerve plexus – lies between the layers of the muscularis, controls peristalsis
  4. Linked to the CNS via afferent visceral fibres, sympathetic and parasympathetic neurons of the ANS also enter the GI tract
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9
Q

Mouth - secretes

A
  1. The mouth of oral cavity is formed by the cheeks, hard and soft platelets, lips, and tongue which aid mechanical digestion
  2. The tongue forms the floor of the oral cavity, it is composed of the skeletal muscle covered with mucous membrane, the superior surface and lateral areas of the tongue are covered with papillae. Some papillae contain taste buds, glands in the tongue secrete lingual lipase which digests triglycerides once in the aid environment of the stomach
  3. Most saliva is secreted by the salivary glands, which lie outside the mouth and release their secretions into ducts that empty the oral cavity. There are three pairs of salivary glands, parotid, submandibular and sublingual. Saliva lubricates food and starts the chemical digestion od carbohydrates, salivation is controlled by the Autonomic nervous system
  4. The teeth project into the mouth and are adapted for mechanical digestion, a typical tooth consists of three principal portions crown, root and neck. Teeth are composed primarily of dentin and are covered by enamel, the hardest substance in the body. Humans have two sets of teeth, deciduous and permanent
  5. Through mastication food is mixed with saliva and shaped into a bolus
  6. Salivary amylase begins the digestion of starches in the mouth
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10
Q

The mouth, pharynx and Oesophagus

A
  1. Food enters the GI tract via the mouth
  2. Oral mucosa is stratified Squamous epithelium
  3. The mucus lubricates the walls of the tract and protects the tissue
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11
Q

Pharynx and Oesophagus

A
  1. Food that is swallowed passes from the mouth into the portion of the pharynx called the oropharynx. From the oropharynx food passes into the Laryngopharynx
  2. The oesophagus is a muscular tube that connects the pharynx to the stomach
  3. Swallowing moves a bolus from the mouth to the stomach by peristalsis. It consists of a voluntary stage, pharyngeal stage and oesophageal stage
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12
Q

The tongue - what is it, covered and muscles

A
  1. The tongue is a mucosa covered skeletal muscle, intrinsic muscles allow it to change shape, extrinsic muscles allow it to change position
  2. Cranial nerves X11 supplies muscle
  3. Cranial nerves V11 and X1 allow taste
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13
Q

Functions of the tongue

A
  1. Mastication
  2. Deglutition
  3. Speech
  4. Taste
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14
Q

Salivary glands

A
  1. Saliva moistens and cleanses the mouth, moistens food, promotes taste, veins digestion of strange (amylase) facilitates speech
  2. Salivation is stimulated by parasympathetic reflex and by activation of chemical and pressure receptors in the mouth
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15
Q

Pairs of salivary glands

A
  1. The parotid – each side of the face
  2. The submandibular – found on each side of the face under the jaw
  3. The sublingual – these lie under the membrane of the floor of the mouth
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16
Q

The teeth - contain

A
  1. 20 deciduous teeth begin to develop and replaced by 32 adult teeth
  2. Closed as incisors, canines and premolars and molars
  3. Each tooth has an enamel covered crown and a cementum covered root
  4. The bulk of the tooth is dentin, which surrounds the bulk cavity
  5. Teeth function to masticate food
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17
Q

Oesophagus - extend and found

A
  1. The Oesophagus extends from the Laryngopharynx to the stomach
  2. 25cm long with 2cm diameter
  3. Found in front of the vertebral column and behind the trachea
  4. Just below the diaphragm it joins the stomach
18
Q

The stomach - areas, layers and connects

A
  1. (The stomach is divided into 3 areas – the Fundus, the body, the antrum)
  2. (The stomach has 3 layers of muscle – the outer layer (longitudinal layer), the middle layer (circular muscle), the inner layer (oblique muscle)
  3. (And extra layer allows for the churning motion)
  4. (The stomach connects the oesophagus to the duodenum.)
19
Q

Gastric juice - how much secreted

A
  1. About 2l of gastric juice are secreted daily
  2. Water and mineral salts are secreted by gastric cells
  3. Mucus secreted by goblet cells
  4. Hydrochloric acid and intrinsic factor secreted by parietal cells in the gastric glands
  5. Inactive enzyme precursors – pepsinogens secreted by chief cells in the glands
  6. (Secreted by the stomach glands and aid in digestion)
20
Q

Phases of digestion

A
  1. Gastrin - produced in the stomach mucosa – stimulant of stretching the stomach, partially digested proteins and caffeine in stomach and high pH of stomach chyme – stimulates secretion of gastric juice, increases motility of GI tract and releases pyloric sphincter
  2. Secretion – produced in the intestinal mucosa – stimulant of acidic chyme that enters the small intestine – stimulates secretion of pancreatic juice rich in bicarbonate ions
  3. Cholecystokinin – produced in the intestinal mucosa – stimulant of amino acids and fatty acids in chyme in small intestine – inhibits gastric emptying, stimulates secretion of pancreatic juice rich in digestive enzymes, causes ejection of bile from the gallbladder and induces a feeling of satiety (feeling full)
21
Q

The small intestine

A
  1. The small intestine extends from the pyloric sphincter to the ileoceal sphincter, it is divided into the duodenum, the Jejunum and the ileum
  2. The small intestine is highly adapted for digestion and absorption, its glands produce enzymes and mucus and the microvilli, villi and circular folds of its wall provide a large surface area for digestion and absorption
  3. Mechanical digestion in the small intestine involves segmentations and migrating waves of peristalsis
  4. Enzymes in pancreatic juice, bile and the microvilli of the absorptive cells of the small intestine break down disaccharides to monosaccharides, protein digestion is completed by peptidases, triglycerides are broken down into fatty acids and monoglycerides by pancreatic lipase, and nucleuses break down nucleic acids to peptides and nitrogenous bases
  5. Absorption is the passage of nutrients from digested food in the gastrointestinal tract into the blood or Lympth, it occurs mostly in the small intestine by means of simple diffusion, facilitated diffusion osmosis and active transport
  6. Monosaccharides, amino acids and short chain fatty acids pass into the blood capillaries
  7. Long chain fatty acids and monoglycerides are absorbed as part of the micelles, resynthesized to triglycerides and transported in chylomicrons to the lacteal of a villus
  8. The small intestine also absorbs water, electrolytes and vitamins
  9. The small intestine is continuous with the stomach at the pyloric sphincter
  10. Over 5m long
  11. Made of 3 sections
  12. The duodenum is about 25cm long and curves around the head of the pancreas
  13. Secretion from the gall bladder and pancreas are released into the duodenum via the hepatopancreatric ampulla
  14. The Jejunum is the middle section and around 2m long
  15. The ilium is the terminal section is about 3m long and ends at the ileocaecal valve
  16. Circular folds, villi and microvilli increase the intestinal surface area for digestion and absorption
  17. Major digestive and absorption organ
  18. Intestinal juice is largely water with a few enzymes, controlled by stretch and chemicals
22
Q

Absorption of nutrients

A
  1. Diffusion – monosaccharides, amino acids, fatty acids and glycerol diffuse slowly down the concentration gradient
  2. Active transport – monosaccharides, amino acids, fatty acids and glycerol may be actively transported into the villi this is faster than diffusion
23
Q

Large intestine

A
  1. The large intestine extends from the ileocecal sphincter to the anus, its regions include the cecum, colon, rectum and anal canal
  2. The mucosa contains numerous absorptive cells that absorb water and goblet cells that secrete mucus
  3. Mass peristalsis is a strong peristaltic wave that drives the contents of the colon into the rectum
  4. In the large intestine substances are further broken down and some vitamins are synthesised through bacterial action
  5. The large intestine absorbs water, electrolytes and vitamins
  6. Feces consist of water, inorganic salt, epithelial cells, bacteria and undirected foods
  7. The elimination of feces from the rectum is called defecation which is a reflex action aided by voluntary contractions of the diaphragm and abdominal nucleus and relaxation of the external anal sphincter
  8. Consist of the caecum and appendix, colon (ascending, transverse, descending and sigmoid portions), rectum and anal canal. It opens to the body exterior at the anus
  9. Functions of the large intestine include absorption of water, electrolytes and some vitals and defecation
24
Q

Internal anal sphincter -
External anal sphincter -

A
  1. Smooth muscle - autonomic nervous system (involuntary)
  2. Striated - somatic nervous system (voluntary)
25
Q

Movement in the colon

A
  1. Peristalsis
  2. Colonic segmentation in haustrae
  3. Mass movements
  4. Local reflexes
26
Q

Defaecation

A
  1. A complex act involving both voluntary and reflex actions
  2. Rectum has a rich sensory supply
  3. Internal anal sphincter muscle maintains a tonic contraction
27
Q

Faecal continence is maintained by

A
  1. Integrity of the anal sphincters
  2. Pelvic floor muscles
  3. Anal cushions
  4. Nervous control of the anal canal and pelvic floor
  5. The consistency of faeces
  6. Healthy rectum
28
Q

The pancreas

A
  1. Is a place grey lands weighing 60g
  2. It is about 12-15cm long and is situated in the epigastric and left hypochondriac region
  3. It consists of a broad head a body and narrow tail
  4. The pancreas is both an exocrine and endocrine gland
  5. Secretions pass from the pancreas to the duodenum via the pancreatic duct
  6. Pancreatic islets secrete hormones and constitute the endocrine portion of the pancreas
  7. Acini which secret pancreatic juice, constitute the exocrine portion of the pancreas
  8. Pancreatic juice contains enzymes that digest starch (pancreatic amylase), proteins (trypsin, chymtrypsin and carboxypeptidase), triglycerides (pancreatic lipase) and nucleic acids (ribonuclease and deoxyribonuclease)
29
Q

The endocrine pancreas

A
  1. Inside the pancreas are specialised cells called pancreatic islets
  2. The islets have no ducts so the hormone diffuses directly into the blood
  3. The endocrine pancreas secretes the hormones insulin and glucagon which are concerned with the control of blood glucose levels
30
Q

The liver

A
  1. Largest gland in the body
  2. weights between 1-2.3kg
  3. Occupies the right hypochondriac region
  4. Upper and anterior portions are smooth to fit under the surfaces of the diaphragm
  5. The liver is enclosed by a thin inelastic capsule and completely covered by a layer of peritoneum
  6. The liver has 4 lobes
  7. The large right lobe
  8. The smaller wedge shaped left lobe
  9. The other 2 lobes are the caudate and Quadrate lobes on the posterior surface
  10. The portal fissure is where various structure enter and leave the liver
  11. The portal vein enters carrying blood from the stomach, spleen, pancreas, small and large intestine
  12. The hepatic artery carries arterial blood
  13. Nerve fibres both sympathetic and parasympathetic enter
  14. Lymph vessels leave the liver, draining Lymph to abdominal and thoracic nodes
31
Q

Structure of the liver

A
  1. The lobes of the liver are made up of tiny functional units called lobules
  2. Each lobule is hexagonal in outline and are formed by cubical shaped cells the hepatocytes which are arranged in pairs of columns and radiate form a central vein
  3. In between the columns are sinusoids (blood vessels with incomplete walls)
32
Q

Functions of the liver

A
  1. Carbohydrate and metabolism – the liver has an important role in maintaining plasma glucose levels, after a mean glucose is converted to glucagon for storage under the influence of the hormone insulin
  2. Later when glucose levels fall the hormone glucagon stimulates conversion of glucagon into glucose again
  3. Fat metabolism – stored fat can be converted to a form that can be used as energy by the cells
33
Q

Blood and liver

A
  1. Portal vein (deoxygenated blood rich in nutrients)
  2. Blood in liver – interlobular vein, sinusoid (hepatic artery), central vein
  3. Blood after leaving the liver – hepatic vein, inferior vena cava, right atrium of the heart
34
Q

Liver and gallbladder

A
  1. The liver has left and right lobes. The gallbladder is a sac located in a depression under the liver that stores and concentrates bile produced by the liver
  2. The lobes of the liver are made up of lobules that contain hepatocytes (liver cells), hepatic sinusoids, reticuloendothelial cells and central vein
  3. Hepatocytes produce bile which is carried by a duct system to the gallbladder for concentration and temporary storage
  4. Biles contribution to digestion is the emulsification of dietary lipids
  5. The liver also functions in carbohydrate, lipid, and protein metabolism processing of drugs and hormones, excretion of bilirubin, synthesis of bile, salts, storage of vitamins and minerals, phagocytosis and activation of vitamin D
35
Q

Bile

A
  1. Emulsifies large fat particles I food into microscopic particles and the increased surface area allows lipase enzymes secreted in pancreatic juice to digest lipids
  2. Waste products such as bilirubin and end product if haemoglobin destruction and excesses of cholesterol are excreted in bile
36
Q

Bile released into the intestine

A
  1. Bile is concentrated and stored In the gallbladder
  2. After a meal is eaten fatty acids In the lumen of the duodenum stimulate endocrine cells to release the hormone cholecystokinin
  3. CCK produced In the walls of the duodenum stimulates the smooth muscle of the gallbladder to contract allowing bile to be released into the duodenum
37
Q

Composition of bile

A
  1. Water
  2. Mineral salts
  3. Mucus
  4. Bile salts
  5. Bile pigments
  6. Cholesterol
  7. Lecithin
38
Q

Bile salts

A
  1. Made from cholesterol
  2. Act like detergents and breakdown fat go unless into tiny, microscopic droplets
  3. Bile salts involved in transport and absorption of fat soluble vitamins
  4. Amongst the cells lining the sinusoids are hepatic macrophages which destroy damaged cells and foreign particles that may be in the blood
  5. Blood then drains into the central vein
  6. These veins join to form larger veins which eventually form the hepatic vein
  7. Which leave the liver and drain into the inferior vena cava
39
Q

Secretion of bile

A
  1. The hepatocytes synthesise the constituents of bile from the mixed arterial and venous blood in they sinusoids, these include bile salts, bile ligaments and cholesterol
  2. Storage, include glucagon, fat soluble vitamins, iron, copper, water soluble vitamins
40
Q

Protein metabolism

A
  1. Deamination of amino acids
  2. Removes the nitrogenous portion of the amino acid forming urea which is excreted
  3. Breaks down nucleic acids to form Uric acid which is excreted
  4. Transamination removes the nitrogenous portion of the amino acid forming new non essential amino acids
  5. Synthesis of plasma proteins – most blood clotting factors are made from amino acids
  6. Breakdown of erythrocytes and defence against microbes carried out by phagocytise hepatic macrophages
  7. Detoxification of drugs and noxious substances, these include alcohol and toxins from microbes
  8. Inactivation of hormones, these include insulin, glucagon, cortisol, aldosterone, thyroid and sex hormones
  9. Production of heat, the liver uses a lot of energy and produces a lot of heat

NURX1003 (24 decks)

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