Digestive System 5

Question 1

What is the portal vein?

Answer 1

takes nutrient rich blood to liver for processing

Question 2

What happens to Absorbed carbohydrates and proteins in the SI?

Answer 2

Absorbed carbohydrates and proteins:

• Move from interstitial fluid into blood capillaries.
• Smaller blood vessels join to form portal vein circulating to liver.

Question 3

What happens to Absorbed fats (chylomicrons) in the SI?

Answer 3

Absorbed fats (chylomicrons):

• Too large to enter blood capillaries so move from interstitial fluid into lacteal (lymphatic capillary).
• Once in lacteal flows into other lymphatic vessels eventually enters bloodstream near subclavian veins circulating to liver and adipose.

Question 4

What is Metabolic Rate?

Answer 4

rate at which energy is used for metabolic reactions

Question 5

What is Anabolism?

Answer 5

building reactions

Question 6

What is Catabolism?

Answer 6

breakdown reactions.

Question 7

Nutritional State

What is the Absorptive State?

Answer 7

Absorptive – fed state – during and shortly after meals.

• Glucose: for energy, glycogen storage.
  Excess is converted to fat – adipose storage.
• Amino acids – proteins / converted to ketoacids (energy needs or excess converted to fat – adipose storage).

glycogen storgae in liver/muscles

Question 8

What is Adipose Storage?

Answer 8

Fat – adipose storage

Question 9

Nutriotonal State

What is the Postabsorptive State?

four

Answer 9

Postabsorptive – fasted state – between meals.

• Glycogen: broken down for energy needs.
• Glucose – formed from other molecules (ketoacids, lactate, glycerol) – energy needs.
• Other substances: fats, lactate, ketones (from fatty acids) are broken down for energy needs – spare glucose.
• Proteins – broken down to amino acids – source of ketoacids and energy needs.

Question 10

Adipose

Answer 10

Adipose tissue is a specialized type of connective tissue that functions primarily as a storage site for energy in the form of fat. The main role of adipose tissue is to store excess energy in the form of triglycerides and release it when needed for various physiological processes. Adipose storage plays a crucial role in energy homeostasis in the body.

Question 11

What is Basal metabolic rate (BMR)?

Answer 11

Energy needed to perform only most essential activities

Question 12

What is Total Metabolic rate?

breakdown

Answer 12

Total daily energy expenditure.

• BMR: 60% of TMR.
• Physical activity: 30-35% of TMR.
• Food-induced thermogenesis (digestion, absorption, storage): 5-10% of TMR

Question 13

Since Metabolic Activities produce heat, how does the body regulate body Temperature?

Answer 13

Homeostasis around a core temperature:

• If core temperature decreases – produce or conserve heat – vasoconstriction especially in extremities, release epinephrine/norepinephrine/thyroid hormones, shivering.
• If core temperature increases – lose heat – vasodilation especially in extremities, decrease metabolic rate, sweat evaporation

Question 14

What is the Ileocecal valve?

Answer 14

Ileocecal valve – controls entry into large intestine (cecum).

• Valve mostly closed;
  relaxation needed to enter large intestine

Question 15

Neural

What is the Gastroileal reflex?

Answer 15

Stimuli – bolus and mixing waves in stomach trigger:

• Increases segmentation in ileum.
• Relaxes ileocecal valve.
• Moves previous material from small to large intestine in preparation for new material arrival

Question 16

Hormonal

What is the Gastrin Reflex?

Answer 16

Gastrin can also relax ileocecal valve

Question 17

Chemical Digestion in Large Intestine:

Answer 17

Secretions are minimal and lack digestive enzymes –

mostly mucus and water secretion for lubrication and formation of feces

Question 18

Bacterial digestion in Large Intsetine:

Answer 18

Bacterial flora (10 million discrete types): “microbiome”

• Ferment some undigested carbohydrates – gases
• Convert some undigested fiber to short chain fatty acids.
• Produce small amounts of vitamins (vitamin B complex and vitamin K)

Question 19

What are the Functions of the Large Intestine?

Answer 19

• Absorption – some water and electrolytes / bacterial products (~10% of absorption in large intestine).
• Storage – non-absorbed material in distal large intestine till defecation.
• Typically ~12 – 24 hours in large intestine.

Question 20

What is Haustral churning?

Answer 20

Haustral churning is the movement of the contents within the haustra, which are the pouches or segments of the large intestine.

This churning helps mix the contents, bringing them into contact with absorptive surfaces and facilitating the absorption of water and electrolytes.

Question 21

What is the Goal of Haustral Churning?

Answer 21

Motility: The primary goal of haustral churning is to mix the material in the haustra and bring it in contact with the absorptive surfaces of the colon

Question 22

What occurs once the Haustra is Filled?

Answer 22

Distension Response: When a haustrum fills with material, the walls of the haustra stretch or become distended.

Smooth Muscle Contraction: In response to the distension, the smooth muscle in the wall contracts. This contraction pushes the material to adjacent haustra, contributing to both backward and forward movement

Question 23

How does Haustral Churning Vary through differnt parts of the LI?

Answer 23

In addition to churning, there is a propulsive movement that helps propel the contents through the large intestine.

Stronger haustral churning occurs in the early parts of the large intestine compared to later portions

Question 24

What is the Strength of Peristalsis in the LI?

Answer 24

Weak peristalsis
Motility – propulsive

Question 25

Mass movements In Large Intestine:

Answer 25

Mass movements are propulsive movements that occur approximately 3 - 4 times a day.

These movements involve intense peristalsis, particularly from the transverse colon to the rectum (aka “sweeping”)

Question 26

What Stimulates Mass Movement in the LI? What does this lead to?

Answer 26

Gastrocolic Reflex (Neural):
A neural reflex triggered when a bolus enters the stomach. This reflex initiates the movement of previous materials from the large intestine to the rectum, preparing the rectum for the arrival of new material.

Gastrin (Hormonal):
can also serve as a trigger for mass movement

Often leads to urge to defecate.

Question 27

What is the Defecation Reflex?
What Triggers it?

Answer 27

The defecation reflex is a physiological process that leads to the elimination of feces from the rectum.

The reflex is initiated when the wall of the rectum is distended, typically due to the presence of feces.

Question 28

What detects the distension during the Defecation reflex? Where does it send the Signal to?

Answer 28

Rectal wall distension detected by mechanoreceptors.

“Urge to defecate” signal sent to medulla oblongata and spinal centers

Question 29

What is the Response during the Defecation Reflex?

Answer 29

The rectum contracts.

Simultaneously, the internal anal sphincter relaxes.

The external anal sphincter initially contracts, maintaining voluntary control over defecation.

Question 30

How does change in Pressure Aid in the defecation reflex?

Answer 30

1. As the rectum contracts, pressure builds up in the rectal area
2. Once the pressure in the rectum reaches a certain threshold, the external anal sphincter begins to relax
3. Full relaxation of the external anal sphincter allows for the passage of feces.
4. With the relaxation of the external anal sphincter, feces are voided from the rectum through the anus.

Question 31

How can we have Voluntary control (learned behaviour) over defecation?

Answer 31

Higher Brain centers can override external anal sphincter relaxation

Under these conditions, contraction of rectum moves material from rectum back into sigmoid colon reducing stretch of rectal walls.

Once material is back in sigmoid colon, the rectum relatively empty so “urge to defecate” signal goes away temporarily.

As contents come back into rectum over time defecation reflex cycle starts again.

Restart “urge to defecate” signal to medulla oblongata and spinal centers.