Absorption + Excretion in Digestion Flashcards
What is absorption?
movement of molecules from GIT into blood stream - occurs in the small intestine
large folds in the intestine have finger-like projections (villi) which contain: (2)
- blood supply aiding in absorption
- lacteal which drains into lymph vessel for absorption of fats
epithelial cells line the ____ and have microscopic projections (microvilli) → brush border
villi
Villi + microvilli → large surface area to _____ rate of nutrient absorption
increase
Transport across epithelial cells → can be ____ or passive
active
What energy does active transport require? (2)
Active transport requires energy allowing more nutrients to be transport unlike diffusion alone.
Monosaccharides + amino acids + peptides + vitamins + glucose molecules are actively transported/pumped against their concentration gradient into the epithelial cells from where they enter the bloodstream.
Disaccharides are broken down into monosaccharides via _________ found on the brush border of epithelial cells lining the small intestine.
disaccharidase
How is Glucose + Galactose absorbed? (5)
- absorbed via secondary active transport/co-transport with Na+
- move against a concentration gradient from low concentration in the lumen to high concentration in cells
- SGLT – sodium-glucose linked transporter protein → facilitates secondary active transport (requires some energy)
- Using energy created by the sodium gradient which is created by the sodium-potassium pump → sodium is actively pumped out of the cell and potassium into the cell by using ATP
- Glucose (moves against CG) is coupled with sodium (moves down CG)
How is fructose absorbed? (3)
- Absorbed by cells via facilitated diffusion → No energy involved, passive
- Protein in the membrane allows fructose to move across the phospholipid bilayer
- Fructose moves down the concentration gradient therefore concentration is lower inside the cell
Monosaccharides absorbed enter the blood by ____ _____ moving down the concentration gradient.
facilitated diffusion
How are proteins absorbed?
- Proteases break down proteins into peptides which are further broken down by the membrane-bound
peptidases into free amino acids or slightly larger molecules. - Amino acids undergo secondary active transport/co-transport coupled with Na+. The energy comes from the
sodium-potassium pump. Na+ moves down its CG, while the coupled amino acids move against their CG
into the cells. - Short chains of amino acids (dipeptide/tripeptides) undergo secondary active transport coupled with H+. The short chains go against their CG while the H+ go down their CG. This H+ gradient is established +
maintained by a sodium-hydrogen exchange protein. - In the cell, the short chains of peptides are broken done into free amino acids via peptidases. Some amino acids can be used to form enzymes to aid in digestion. Most amino acids move across the basal membrane out of epithelial cells by secondary active transport or facilitated diffusion into the bloodstream.
- Small amounts of intact proteins can cross the epithelium via endocytosis into the cell and then out of the cell via exocytosis.
(- This occurs within infants
- Before infant can have fully functional immune
response, it relies on the antibodies to be absorbed
from mother’s milk)
What is the hepatic portal vein?
How does the absorption of lipids take place?
- Bile salts are secreted in duodenum to emulsify lipids
making the lipid globules smaller to increase SA on
which lipase can act - Pancreatic lipase breaks down triglycerides to form
free fatty acids + monoglycerides → hydrophobic - Micelles → tiny spheres with fatty core and
hydrophilic exterior allowing them to come to close to
epithelial cells lining of the small intestine - These fatty acids + monosaccharides which are
brought close to the lining are absorbed and reform
into triglycerides within the cells. - Triglycerides then combine with cholesterol + protein
+ phospholipids = chylomicron (lipoproteins) - These chylomicrons form secretory vesicles and exit
the cells via exocytosis, entering the lacteals,
combining to form lymph vessels, where they are
carried away by the lymph, getting drained into the
circulatory system by the subclavian vein
What is the large intestine? (2)
- Begins at ileocecal junction, the last part of the small intestine (ileum) passes into the first part of the large
intestine (cecum) via the ileocecal valve. - Chyme passes through the ascending colon, transverse colon, descending colon, sigmoid colon, into the
rectum, out of the anus.
What are the components of the large intestine? (6)
the ascending colon
transverse colon
descending colon
sigmoid colon
rectum
anus
What is the function of the cecum?
acts as a pouch for chyme from small intestine, absorbs salts + electrolytes from the chyme.
What is the function of the appendix?
attached to the cecum, a vestigial organ however produces + stores good microbes and plays a minor role in immunity.
Moves along colon via ______ and becomes more solid as it moves because the colon completes the reabsorption of water.
peristalsis
How is water absorbed?
Occurs via osmosis through the cells walls into
vascular capillaries inside villi. Water is coupled to
solute absorption.
Most reabsorption occurs in small intestine. Large
intestine finishes reabsorption.
What is the rectum? (2)
- Terminal portion of the large intestine
- Faeces are stored until they may be eliminated
from the anus
2 anal sphincters:
- Involuntary internal sphincter
- Voluntary external sphincter
What happens the rectum fills?
When rectum fills up, signal is sent to brain causing your involuntary internal sphincter to relax, pushing the faeces down. When you are ready, you voluntarily relax yoru external spincter to allow faeces to pass out the anus.
How is digestion regulated?
Each step in digestive system is activated only when needed.
These secretions and motility of the digestive tract are controlled by neural, endocrine and paracrine mechanisms.
External stimuli (sight, smell of food making gastric juices getting released before food reaches it) can also
stimulate _____receptors which can have an effect on the cephalic brain, also influencing the control of_____.
If the cephalic brain or _____________ neurons are involved, which are outside the enteric nervous system, the reflex is called a long (vagovagal) reflex as it involves the _____.
sensory
GIT
parasympathetic/sympathetic
CNS
How is appetite regulated? (2)
- Appetite regulation is a number of homeostatic
mechanisms that control the body’s storage and
metabolism of fat. - Hormones that play a role in appetite regulation
target the satiety centre in the hypothalamus in the
brain.
What is feasting?
Feasting: excess energy is stored as glycogen in liver and muscle cells, additional excess energy is stored in
fat in adipose cells.
What is fasting?
Fasting: body expends liver glycogen, then draws on muscle glycogen and fat .
Since glucose is a major fuel for cellular respiration and a key source of biosynthesis, maintaining blood
glucose concentration within the normal range is critical.
How is homeostasis maintained?
What is a healthy pancreas?
Healthy: pancreas secretes insulin which binds to receptors on liver or muscle cells, allowing for insulin to
be taken into the cells, stored as glycogen.
What is type 1 diabetes?
Type 1: autoimmune disease as pancreas fails to produce insulin “insulin dependent” (can be treated by injecting insulin). No insulin is bound to receptors therefore high blood glucose.
What is type 2 diabetes?
Type 2: later onset in life. Insulin is produced but the insulin receptor is less responsive. Cell fails to responds to insulin properly. “insulin resistant”. Occurs due to obesity, sedentary lifestyle. Requires change in lifestyle in order to reduce blood glucose.
