Digestive System 2 Flashcards
5 Functions of the gut
- Motility
- Secretion
- Digestion
- Absorption
- Storage
What are the 2 types of gut control?
Intrinsic control and extrinsic control
What is intrinsic control?
Where the gut controls itself
What is extrinsic control?
Where the gut is controlled by an external factor outside the gut.
What are the 2 types of control that intrinsic control can have?
Neuronal = enteric nervous system
Hormonal = secretin, gastrin, CCK, GIP, Motilin
What are the 2 types of control that extrinsic control can have?
Neuronal = Vagus and Splanchnic Nerves
Hormonal = Aldosterone
Name the 4 parts of the gastrointestinal tract
- Mucosa
- Submucosa
- Tunica muscularis
- Serosa / adventitia
How is gut regulation controlled in the enteric nervous system? What are the 3 inputs?
By input from the:
- luminal receptors
- hormones
- autonomic nervous system
What is the function of the myenteric plexus?
What control is it under?
Regulates motility and muscle action
Under control of the Parasympathetic nervous system
What is the function of the submucosal plexus?
What control is it under?
Regulates local fluid and hormone release
Under control of the parasympathetic nervous system only
What are the 3 main types of luminal receptors?
Mechanoreceptors
Chemoreceptors
Osmoreceptors
What do mechanoreceptors do?
Detect stretch and stimulate contractions
What do chemoreceptors do?
Sense chemical composition of the chyme and regulate pH
What do osmoreceptors do?
Sense osmolarity and control motility and secretions
What are the 2 functional divisions of the autonomic nervous system?
Sympathetic nervous system - fight or flight
Parasympathetic nervous system - rest and digest
Two neurone pathways
Key anatomical features of the sympathetic nervous system:
- Originate at T1 - L2
- Enter the sympathetic chain
- Leave the sympathetic chain
- Synapse at prevertebral ganglia
Key functions of the sympathetic nervous system:
- slow digestive transit
- closes sphincters
- Fight or flight
Key anatomical features of the parasympathetic nervous system:
- Originate at brainstem or S-levels
- Travel to target organ - along vagus nerve
- Synapse at target
Key functions of the parasympathetic nervous system:
- Increases digestion
- Opens sphincters
- Rest and digest
How is gut regulation controlled by the autonomic nervous system?
The sympathetic nervous system:
- decreases digestive secretions
- decreases digestive motility
The parasympathetic nervous system:
- Increases rest and digest
- Increases digestive motility
what does the suffix -crine mean?
= secrete
What does endocrine mean?
= secreted into blood
What does neurocrine mean?
Secreted by nerves
What does paracrine mean?
Secreted by adjacent cells
What does autocrine mean?
Secreted by self
What is the structure of a gut endocrine cell?
- Columnar
- Narrow apex - sensory - exposed to gut lumen
- Wide base - secretory
What are the 3 phases of digestion?
- Cephalic
- Gastric
- Intestinal
What is the cephalic phase?
= in the head - Salivation
- Stimulated by parasympathetic innervation (Cranial nerves)
- Increases blood flow to glands
- Brainstem regulates visual or olfactory (response to sense of smell) salivation
What is the gastric phase?
= in stomach
- Acid production and enzyme secretion
- Sphincter relaxed
- Relaxation of stomach and duodenum - allowing entry of chyme
- Parasympathetic stimulation
- Gastrin - produced by cells in duodenum, stomach and pancreas
- Secretin produced
- Cholecystokinin produced
- Motilin produced
What is the function of Gastrin?
- Increases acid secretion
- Increases pepsinogen secretion
What is the function of Secretin?
- stimulates bile secretion
- Prevents acid secretion
What is the function of cholecystokinin?
- Stimulates bile and pancreatic secretion
- Also affects motility
- Decreases gastric emptying
What is the function of motilin?
- Increases motility/peristalsis in the gut
- Clears tract between meals
What is hunger and satiety controlled by?
=Hypothalamus
–> regulates the basic biological drives related to survival
the 4Fs = Fighting, Fleeing, Feeding, ‘mating’
What are the 2 parts of the hypothalamus that control hunger and satiety?
Ventro medial area = Inhibitory - Satiety centre
Lateral Area = Facilitative - Appetite Centre
What is the name of the hunger hormone? What is its function?
= Ghrelin
= stimulates hunger
How is ghrelin stimulated?
Stimulated by an empty stomach / fasting
Low blood glucose - Sensory input
= appetite stimulated
Where is ghrelin released?
Released by pancreas and stomach
What is the satiety hormone? What is its function?
= Leptin
- Opposes the action of ghrelin - indicates fullness (satiety)
What is leptin produced by?
Produced by fat cells (adipocytes)
How does leptin act on its target?
Crosses the blood brain barrier to reach the hypothalamus
What can occur if leptin stops working?
= severe over eating and obesity
What are 3 other satiety hormones?
- Cholecystokinin
- Peptide YY
- Glucagon - like peptide 1
–> all released in response to food. Neural controls carried by Vagus nerve but may be reliant on hormones.
What is the endocrine section of the pancreas?
The islets of Langerhans
What is located in the islets of Langerhans?
Alpha -cells
Beta -cells
D-cells
What do alpha cells secrete?
= Glucagon
What do Beta cells secrete?
Insulin
What do D cells secrete?
= Somatostatin
–> present throughout pancreas but most abundant in the tail.
When is glucagon secreted?
Secreted when blood glucose level falls.
Triggers breakdown of glycogen into glucose in the liver
When is insulin secreted?
Secreted when blood glucose is high.
Triggers storage of glucose in liver, skeletal muscle and fat cells.
When is somatostatin secreted from D cells?
Secreted induced by low pH.
Supresses the release of hormones from Alpha and Beta cells.
Inhibits gut motility and exocrine secretion.
What is the definition of obesity?
Abnormal or excessive fat accumulation that presents a risk to health.
- A BMI over 25 is overweight.
- Over 30 is obese.
How do you calculate BMI? What are the units of BMI?
= body mass / (height)^2
Units = kg/m^2
What are the categories for BMI
<18.5 Underweight
18.5 – 24.9 Ideal
25 - 29.9 Overweight
>30 Obese
What are alternatives to BMI?
- Waist circumference
- Waist to hip ratio
- Skinfold thickness
- Bioelectrical impedance
- MRI or DEXA
What are some examples of health risks of obesity?
Risks of metabolic, cardiovascular and musculoskeletal disorders and cancers.
Diabetes
Gallbladder disease
Sleep apnea
Cardiovascular disease
Osteoarthritis
Colon cancer
Gout
What are some environmental factors influencing obesity?
Cost of food
Portion size
Type of food
Physical activity
Total energy intake
How can obesity be managed?
Physical activity
Dietary strategies
Medication
Surgery
What are more invasive methods of reducing obesity?
= Bariatric Surgery
- restrictive - reduced stomach size and dietary intake
- malabsorption (bypasses stomach and small intestine)
=Gastric band (restrictive, minimally invasive, adjustable)
=Gastric bypass ( malabsorptive / restrictive, invasive, irreversible)
= Gastric sleeve ( restrictive, invasive, irreversible)
What is saliva?
a product of a number of glands present within and around the oral cavity
What are major salivary glands?
paired and exist away from the oral cavity, draining into the cavity via a long duct –> exocrine glands
What are minor salivary glands?
present throughout the mucosa of the oral cavity
What supplies salivary glands?
innervated by parasympathetic neurones carried in a number of cranial nerves
What are the 3 main salivary glands?
Parotid gland
Submandibular gland
Sublingual gland
What type of secretion does the parotid gland have?
Serous secretion
What type of secretion does the submandibular gland have?
Mixed secretion ( serous and mucous secretion)
What type of secretion does the sublingual gland have?
Mainly mucous secretion
What is the location and function of the parotid gland?
Sits beside the ear
Drains into the vestibule via the parotid duct
Largest of the paired salivary glands
What is the location and function of the submandibular gland?
Sits under the jaw (mandible)
Drains into the floor of the mouth, under tongue.
What is the location and function of the sublingual gland?
Present beneath the tongue.
Drains directly into the oral cavity via a number of small ducts.
Paired gland.
What are the 8 main functions of saliva?
Digestion
Mineralisation
Antimicrobial
Buffering
Lubrication
Agglutination
Gustation
Hydration
What are the functions of saliva in: Digestion
digestive enzymes present in saliva - amylase, mucins, lipases
What are the functions of saliva in: Mineralisation
Proteins within saliva produce protective layer - assists in mineralisation of teeth
What are the functions of saliva in: Antimicrobial
Saliva compounds can kill bacteria e.g amylase, mucins
What are the functions of saliva in: Buffering
a delicate pH balance is needed for digestion and to protect the teeth. Carbonic anhydrase is buffer present in saliva
What are the functions of saliva in: Lubrication
Saliva coats mucosa of the oral cavity
What are the functions of saliva in: Agglutination
Bacteria present in the oral cavity is trapped in saliva
What are the functions of saliva in: Gustation
(tasting) made possible by saliva, detection from taste buds when food is dissolved in saliva
What are the functions of saliva in: Hydration
receptors can detect hydration levels and stimulate desire to drink
