Final (Rachael's Contribution) Flashcards

Question 1

Q

Macronutrients
Micronutrients

Answer

A

Macronutrients: carbohydrates, fats, and proteins
Micronutrients: vitamins, minerals

Question 2

Q

Actions of the Digestive System (4)

Answer

A

Digestion
- Chemical and Mechanical
Absorption
- Epithelial transport
Secretion
- Digestive enzymes, water, mucus, bile, acid, bicarbonate
Motility
- Progression, mixing, regulated passage

Question 3

Q

Internal vs. External Environment

Answer

A

NOT excretion on the list.
- Removal of cellular waste products
- What passes out of anus was never part of the internal environment
- The respiratory and urinary system does some excretion
  - Exception: excretion via bile
    - Cholesterol, bile pigments (breakdown of heme)
Digestive secretions are: exocrine secretions
- Released into the lumen
- Digestive tract is not regulatory in what it absorbs. Wants max absorption. Other factors regulate things like how many calories are taken it.

Question 4

Q

Peritoneum

Answer

A

Serous membrane
Delicate membrane that suspends digestive organs in the abdomen
Consists of tiny layer of connective tissue and then simple, squamous epithelium
Releases fluid
Around organ=visceral peritoneum
Again body wall=**parietal peritoneum **

Question 5

Q

Peritoneal Cavity

Answer

A

Potential space that is created by peritoneum
This is where the fluid is released
In the internal environment of the body
Break of GI tract and bacteria into peritoneal cavity is bad-news-bears
- Called peritonitis

Question 6

Q

Retroperitoneal

Answer

A

Organ not completely surrounded by peritoneum
Ascending and descending colon
- Have adventitia instead (aka: connective tissue)

Question 7

Q

Mesentery

Answer

A

Two peritoneum that come together
Suspend the organs
Place where there is a lot of adipose tissue
Blood vessels
- Superior and Inferior mesenteric arteries

Question 8

Q

Peritoneum Figure

Question 9

Q

Components of the Digestive Tract

Answer

A

Gastrointestinal tract: Tube from mouth to anus
- Accessory organ: Organs that attach to GI tract to release secretions
Mouth and Pharynx:
- Salivary Glands: Moisten, lubricate, polysaccharide digestion
Esophagus:
Stomach: HCl, pepsin, mucus, store, mix, solubalize, protein digestion, lubricate and protect liquid suspension
- **Liver: **bile salts, bicarbonate
- **Gallbladder: **stores bile
**Small Intestine **(duodenum, jejunum, ileum): digestion and absorption, maintain fluidity of luminal contents, lubrication
- **Pancreas: **digestive enzymes, bicarbonate
**Large Intestine: **tiny bit of nutrient absorption, water absorption, concentrating undigested/bacterial material
Rectum

Question 10

Q

What is Bacteria in GI Tract called?

Answer

A

gut microbiome

Question 11

Q

Gut Microbiome: Function

Answer

A

A bit of digestion; nutrient extraction
- Release of vitamin K
Protective
- Vast numbers/competition protect from colonization by pathogenic bacteria
Role in development of immune system

Question 12

Q

Gut Microbiome: Who are they?

Answer

A

Characterized by DNA sequencing
Different species based on what DNA sequences that they are finding
About 400 species

Question 13

Q

Gut Microbiome: How do they get there?

Answer

A

Colonization during birth
Twin have a different pattern of microbiome
Composition influenced by host and by diet
Trends associated with disease

Question 14

Q

Definition: Dysbiosis

Answer

A

Imbalance in gut microbiome that could lead to/exasperate disease

Question 15

Q

Antibiotic Associated Colitis

Answer

A

Wipe out your microbiome
- Also known as C. diff.
Infection with bacterium Clostridium difficile
Pseudomembranous colitis
- Patches on colon that ooze pus
Treat person by replacing with normal fecal microbiota
- Fecal microbiota transplant (FMT)
- 90-95% are cured in one treatment

Question 16

Q

Inflammatory Bowel Disease

Answer

A

Abnormal inflammatory response to gut microbiome
No smoking gun bacteria, might be a host genetic factor
Genes linked to IMD
- Genes involved in innate immunity
- Genes involved in barrier function (characteristics that prevent mucosa from being leaky)

Question 17

Q

Ulcerative Colitis

Answer

A

Is an inflammatory bowel disease
Restricted to the colon
Mucosal inflammation
Continuous lesions

Question 18

Q

Crohn’s Disease

Answer

A

Inflammation anywhere in the GI tract
Interspersed with normal mucosa
Affects mainly the ileum, and anal region
Lesions are transmural
- go through all the layers
Develop fistula
- abnormal connections between GI compartments
Treatments: anti-inflammatory drugs; biologic therapies
- anti-TNFalpha
May be from abnormality in the bacteria that is living in their gut

Question 19

Q

Irritable Bowel Syndrome (IBS)

Answer

A

Like fibromyalgia where people are affected but no one knows why. Increased pain and discomfort

Question 20

Q

Which of the following are continuous with the external environment?

Rectum
Common Bile Duct
Pancreatic Duct
Liver Sinusoid
Peritoneal Cavity

Answer

A

Rectum: Yes
Common Bile Duct: Yes
Pancreatic Duct: Yes
Liver Sinusoid: No (It’s a capillary)
Peritoneal Cavity: **No **

Question 21

Q

Tissue structure of the digestive tract

Answer

A

Layer closest to lumen is mucosa
- 3 subdivisions
Serosa is the peritoneum
Main thing that changes along GI tract is in the mucosa

Question 22

Q

Changes in Mucosa along GI Tract

Answer

A

Esophagus:
- Protective: stratified squamous epithelium, MALT
Stomach:
- Secretory: glands, highly folded simple columnar epithelium
Small Intestine:
- Absorption: highly folded simple columnar epithelium, expanded surface area with villi

Question 23

Q

Why is there absorption in the small intestine?

Answer

A

Very long
Highly folded
- Plicae circulares: see with eyes, folding of entire musocsa
- Villi and crypts: folding of the epithelium
- Enterocyte: (epithelium intestinal cell) apical membrane has microvilli. Individual cell. Only see with electron microscope. Brush border

Question 24

Q

Lacteal

Answer

A

Poking into the villi are capilaries and lacteal
Lacteals:
Lymphatic capillary
Involved in absorption of fats

Question 25

Q

Intestinal Crypts

Answer

A

Where cell division occurs
Some stem cells in the basement of the crypt
Travel up as they age
Cells in the crypt are secretory
Cells on villus are absorptive
- Die at the villus
- Whole epilthelium is renewed every 4-5 days.

Question 26

Q

Carbohydrates: Digestion by A**mylase **

Answer

A

Release by salivary glands and pancreas
Brush Border Enzyme
Undigestable Carb: Fiber
- Hold water, creates bulk, helps motility in the large GI
Poly and disaccharides need to be converted to monosaccharides for absorption
- Start in oral cavity
  - Polysaccharide: acted on by salivary amylase
- Stomach
  - salivary amylase inactivated by low pH
- Small intestine
  - pancreatic amylase, break things down to be small polysaccharides
  - brush border enzymes break down to monosaccharide (sucrase, lactase, etc.)

Question 27

Q

People with no Lactase

Answer

A

Lactose maldigestion, lactose ends up in large intestine
Large intestine:
- Lactose digested by bacteria
- Cause gas
- More solute in large intestine (holds water and generates diarrhea)
Lots of symptoms, call lactose intolerance

Question 28

Q

Carbohydrate Absorption

Answer

A

Co-transport coupled to Na+
Absorption of monnosaccharide and amino acids

Question 29

Q

Protein: Digestion in Stomach

Answer

A

Pepsin just in stomach
- Works best at stomach pH
- Good at taking apart collagen
- Turns proteins into peptides

Question 30

Q

Protein: Digestion in Small Intestine

Answer

A

trypsin, chymotrypsin, carboxypeptidase (pancreatic) and brush border enzymes
Pepsin inactivated (above pH 5)
Enzymes from pancreas
- Digest down to very small peptides
Brush border enzymes
- Down to the amino acid

Question 31

Q

Protein: Absorption

Answer

A

Co-transport coupled to Na+
Co-transport may be couple with a specific amino acid

Question 32

Q

Protein: Endocytosis

Answer

A

Mechanism for passive immunity in infants
Transcytosis
- To absorb intact polypeptides
- Endocytosis at apical surface to bring in protein
- Travel to basolateral membrane and exocytose
Ig-A secreted into breast milk and then absorbed by the infant via transcytosis
Also how antigens travel into the MALT

Question 33

Q

Activation of zymogens

Answer

A

Inactive enzyme precursor
Ex: Chief cell makes pepsinogen
Pepsinogen + Acid → change confirmation and open active site
- Then cleaves pepsinogen to make pepsin
Activation of pancreatic zymogens
Gall stone
- Enzymes get inappropriately activated in pancreas.
- Results in inflammation of pancreas called pancreatitis

Question 34

Q

Fats

Answer

A

Main fat is TAG
When fat digested, TAG goes to monoglyceride and 2 FA
- Via lipase, this enzyme is water soluable
Fat want to associate with itself
- Need to break up fat droplet into many little products
- **Emulsification **

Question 35

Q

Fats: Emulsifying agents

Answer

A

Bile salts, phospholipids
Keeps fat from associating
Bile salt are made from cholesterol in the liver
Amphipathic molecules coat the small emulsion droplets

Question 36

Q

Fats: Digestion

Answer

A

Lipase
Lipase bound to emulsion droplets via amphipathic protein called co-lipase
Co-lipase
- amphipathic, secreted by pancreas, binds lipase, anchors lipase to the surface of emulsion droplets
Digestion occurs in emulsion droplets
Lipase digests TAG to monoglycerides and FA
Fat digestion products associate with bile salts and phospholipids to form micelles

Question 37

Q

Fats: Micelle Formation

Answer

A

Micelles: fatty acids, monoglycerides, bile salts, phospholipids, cholesterol, fat-soluble vitamins
Fat digestion products
At the top are the amphipathic molecules that are in pancreas
4-7 nm→1/200th the size of an emulsion droplet
Micelles ferry fat digestion products to the apical plasma membrane of enterocytes.

Question 38

Q

Fat Emulsion/Digestion Figure

Question 39

Q

Fat: Absorption into Enterocytes

Answer

A

Simple diffusion of freely dissolved monoglycerides and FA
Carrier proteins
Cholesterol absorption
- Cholesterol in SI comes from cholesterol in bile and dietary cholesterol.
- 50% cholesterol in SI is reabsorbed into body and 50% eliminated
- Drug increases cholesterol elimination
  - Ezetimibe: blocks carrier protein for cholesterol (reduces absorption)

Question 40

Q

Fat: Chylomicrons

Answer

A

Lipoproteins
TAG
- Cholesterol
- Fat soluble vitamins
- Phospholipids
- Apolipoproteins
Chylomicrons: lipoproteins produced by enterocytes
- Way that fat is carried around in the circulation
Get into circulation by entering leaky lymphatic capillaries (lacteals), flow via lymphatic vessels and get into circulation
TAG in lipoprotein digested by lipoprotein lipase→monoglyceride and 2 FA that can go into cells

Question 41

Q

Vitamin B₁₂ Absorption

Answer

A

Requires intrinsic factor
Water soluble
Important for cell division, affects RBC products, anemia occurs
Parietal cells in stomach produce intrinsic factor
IF bind to vitamin B12 to make complex
Complex travels to bottom of the SI
Ileum: absorption via receptor-mediated endocytosis
Lack of intrinsic factor (causes B12 deficiency)→prenicious anemia
Autoimmune cells destroys parietal cells
Crohn’s disease causing inflammation in ileum, causing decreased absorption of B12 (causes deficiency)

Question 42

Q

Vitamin Absorption

Answer

A

Fat soluable vitamins→tag along with fat absorption
Water soluable vitamins→carriers, diffusion

Question 43

Q

Iron Absorption

Answer

A

No efficient way to get rid of iron, so needs to be efficiently recycled.
Iron deficiency→anemia
Too much ion: free radical formation→tissue damage
Into enterocyte via DMT-1
- Then can go into 2 different pathways (ferritin or ferroportin)
  - Ferritin
    - not actually in the body because enterocytes overturn readily
Regulated iron absorption occurs in the duodenum
Transferrin: figure out how much iron in body by looking at saturation
- <25% saturated (normally)

Question 44

Q

Regulation of Iron Absorption Responding to 2 Signals

Answer

A

1. Is there a need for iron (w/ regard to bone marrow)
  * Needed because making RBC
  * Don’t know what that signal is
1. Body iron stores (mostly liver, some spleen)→signal (hormone: hepcidin)→act of enterocytes to allow iron absorption
  * When body iron stores full
  - increased hepicidin by liver, travels to duodenum, bind ferroportin, ferroportin internalized and degraded

Question 45

Q

Hemochromatosis

Answer

A

Disorder of iron overload
Mutation in HFE gene
- most common cause
Unregulated iron absorption
- Accumulation of iron in tissue
- form free radicals
- tissue damage
  - Liver, pancreas, heart, joint
Symptoms arise in middle age
Treatment:
- Bleeding to remove iron, phlebotomy
HFE protein thought to be involved in sensing the amount of iron
- When defective
  - iron isn’t sensed properly
  - deficient secretion of hepcidin

Question 46

Q

Iron Absorption: Figure

Question 47

Q

Disruption of Absorption: Celiac Disease

Answer

A

Inappropriate immune response to gluten
- Involves CD4+ helper T Cells
Not an allergy b/c not atopic disorder
Duodenal biopsy to diagnose celiac disease
- Flattened mucosa (no villi)
- Inflammation
- Increased lymphocytes
Normal small intestine mucosa
Decreased iron absorption
Decreased folate
Anemia will occur
In lamina propia MALT engulf those peptides and display them on their surface
Consequences:
- Malabsorption
- Diarrhea
- Anemia (iron deficiency)

Question 48

Q

Celiac Disease: Figure

Question 49

Q

Disruption of Absorption: Bariatric Surgery

Answer

A

Weight loss surgery
The two most common bariatric surgery procedures are Roux-en-Y gastric bypass and **adjustable gastric banding **

Question 50

Q

Adjustable Gastric Banding

Answer

A

Small pouch created so person feels full more quickly
Restricted procedure

Question 51

Q

Roux-en-Y (RYGB)

Answer

A

Combine restrictive and malabsorptive
Small pouch at fundus is created; piece of SI is brought up and joined to the pouch. Creates a tiny stomach and channel that food flows down.
Stomach left there so that secretions from liver, stomach and pancreas still go SI
Duodenum is powerhouse of absorption, so food bypasses this.
- can cause micronutrient deficiency (like anemia)
Alimentary channel is where the food is. The biliopancreatic channel is where the secretions are.
Length of common channel determines the degree of absorption/malabsorption
For reasons not well understood endocrine changes occur that can achieve remission from Type 2 diabetes
- 75-80% who have DM2 achieve remission

Question 52

Q

Hypothesis of RYGB Endocrine Alteration

Answer

A

Start to have changes in responsiveness and occur even before the profound weight loss
Hypothesis #1:
- There might be an upper GI hormone that is involved in glucose homeostasis
Hypothesis #2:
- Food quicker to lower small intestine
  - Stimulates **endocrine L cells **
  - Release GLP1 and PYY
  - GLP1 increases insulin secretion, decreases glucagon secretion, increasing satiety

Question 53

Q

Digestive Tract Enteric Nervous System

Answer

A

Branch of autonomic nervous system
Neurons in wall of GI tract controlling behavior
Can work in isolation from the CNS
Afferent neurons responding to changes in GI tract
- Chemical sensors
- Stretch sensitive sensors
Efferent neurons→projecting to secretory cells, smooth muscle
Interneurons: connecting and coordinating neurons
Vagus nerve inputs (parasympathetic part of ANS)
submucous plexus
- deeper than the myenteric plexus
myenteric plexus
- Between muscle layers regulating motility
- More neurons

Question 54

Q

Digestive Tract Electrical Activity in Smooth Muscle

Answer

A

Cells are spontaneously active in smooth muscle
Cells are electrically coupled into groups so that they work in concert.
- Via gap junctions
Spontaneous activity in specialized smooth muscle cells (pacemaker cells) produces the basic electrical rhythm
- Spontaneous activity makes the slow waves (“basic electrical rhythm”)
- Electrical coupling causes region to have the oscillating membrane potential
Slow waves with spikes of action potentials
- In the stomach there are 3 waves/min
- Duodenum: 12/min
- Ileum: 9/min
Action potential lets calcium in that regulates muscle contractions (More calcium, stronger contraction)
Slow wave frequency: contraction frequency
Number of action potentials (@ peak): contraction strength
Excitatory input makes the cell more depolarized so that when slow wave reaches the peak, there will be more action potentials
Skeletal muscle only input is somatic efferent
Smooth muscle can have a variety of inputs (more complex):
- Neurons
- Hormones
- Excitatory or inhibitory
- Spontaneous activity

Question 55

Q

Digest Tract Electrical Rhythm Figure

Question 56

Q

gastrointestinal hormones and paracrines

Answer

A

Endocrine cells are generally in the epithelium
Internal secretion, hormone going to the blood stream
Important hormones: gastrin, cholecystokinin (CCK), secretin, incretins (GLP-1, GIP)
Important paracrines: histamine, somatostatin, serotonin
Change in lumen→triggers secretion
- Causes feedback regulation of lumen of GI tract
Often act as growth factors

Question 57

Q

phases of gastrointestinal control

Answer

A

phase=location of stimulus

cephalic phase (cephalic=head)
- stimuli: sight, smell, taste, chewing
gastric phase (gastric=stomach)
- food in stomach
- stimuli: stomach distension, acidity, peptides
intestinal phase
- stimuli: distension, acidity, osmolarity, digestive products

Question 58

Q

salivation

Answer

A

Release saliva in response to food in the mouth
Amylase to digest carbohydrate (from serous acinus)
Also antibacterials
Mucus from mucus acinus

Question 59

Q

Swallowing: 3 Phases

Answer

A

Oral (buccal) Phase
Pharyngeal Phase
Esophageal Phase

Question 60

Q

Oral Phase of Swallowing

Answer

A

Food in mouth
Swallowing is voluntarily initiated
Retracted tongue: push food to the pharynx
- Food in pharynx triggers pharyngeal sensory neurons that project to brainstem nuclei that coordinate the other two phases
Elevation of soft palate so no food up the nose

Question 61

Q

Pharyngeal Phase of Swallowing

Answer

A

Area common to breathing and eating
Inhibit respiration
Glottis muscles close breathing
Larynx elevated to tip the epiglottis down so the trachea is covered

Question 62

Q

Esophageal Phase of Swallowing

Answer

A

Esophageal sphincters relax to allow food to pass
- One at top and one at bottom
Smooth muscle engages in propulsive movement
- peristalsis

Question 63

Q

Swallowing Picture

Question 64

Q

Vomiting Figure

Answer 58

A

Technical term is emesis
Nausea not well understood (can’t use animal models and ask how they feel)
Strong contractions of abdominal muscle to increase abdominal pressure
Relaxation of esophageal muscle
Reverse peristalsis
automatic behavior controlled by nuclei in the brainstem, referred to as the vomiting center
During retching, the lower esophageal sphincter relaxes, abdominal skeletal muscles contract, and strong peristaltic contractions of the muscularis externa operate in reverse of the normal pattern, forcing the contents of the stomach and even the small intestine upward into the esophagus
Emesis occurs when these contractions are strong enough to expel the contents of the GI tract past the upper esophageal sphincter.

Answer 59

A

Irritant in GI tract affects cells that release serotonin
- Serotonin acts as paracrine
- Excites afferents in vagus nerve
- Up to the vomiting center in brain
Toxin in circulation
- Act of area postrema in the brain
  - project to and activate vomiting center
- Also the chemoreceptor trigger zone
- At the posterior end of the 4th ventricle
- Outside the BBB
CNS
- Blow to head can trigger vomiting
- Vestibular mismatch

Answer 60

A

Post operative nausea and vomiting
- opiods and anethestics
- activate opiod receptors in area postrema
Chemotherapy induced nausea and vomiting
- serotonin release of intestinal epithelium
- Free radical formation release serotonin
Treated prophylactically with antiemetic

Answer 61

A

Serotonin antagonist: Zofran and palonosetron (Aloxi®)
- Bind to serotonin receptors 5HT3 antagonists
Substance P antagonists: Aprepitant (Emend)
- P involved in inflammatory pain pathways
- Very effective in limiting vomiting
Antagonists for dopamine, histamine and acetylcholine
- dopamine antagonists promethazine (Phenergan®) and prochlorperazine (Compazine®)
- histamine anatagonist dimenhydrinate (Dramamine®)
- muscarinic anatagonist scopolamine
Cannabinoid agonists such as tetrahydrocannabinol (THC; the principal psychoactive ingredient in marijuana) are also used to reduce nausea and vomiting

Answer 62

A

Upper sphincter limits air into the GI tract (if gets in there, belching)
Factors that increase risk of gastroesophageal reflux:
- decreased tone in lower esophageal sphincter
- increased abdominal pressure (pregnancy, obesity, overeating )
- hiatal hernia
  - When a piece of the stomach fundus goes through the “hiatus” (the hole in the diaphragm)
  - Diaphragm normally reinforces lower esophageal sphincter
GERD Treatments:
- Suppression of acid secretion

Answer 63

A

The mucosa changes with continual exposure to acid
Columnar epithelium appears reddish (abnormal appearance)
Confirmation:
- Biopsy to look for intestinal metaplasia: mucosal change where you see columnar epithelium where it should be stratified squamous. Will see goblet cells
Increased risk for esophageal adenocarcinoma
- May need increased surveillance if known Barrett’s esophagus

Answer 64

A

Functions:
- Solubilizes food
- Pepsin activity
- Kills bacteria
Parietal cells secrete HCl acid
- H+/K+ ATPase-“proton pump”
- Apical plasma membrane
Stimulation of acid secretion: translocation of proton pumps to apical plasma membrane

Answer 65

A

Stimulation of acid secretion: translocation of proton pumps to the apical plasma membrane
Regulators:
- Neurotransmitter: acetylcholine
  - Released from enteric neurons
- Paracrine: histamine
  - Released from ECL cells
- Hormone: gastrin
  - Released by G cells in gastic epithelium
  - Stimulates ECL cells to increase histamine (indirect effect)
  - Stimulates proliferation of parietal cells (direct effect)
- Negative Regulator:** Somatostatin**
  - secreted by endocrine cells of the gastric epithelium
  - Acts as both a paracrine and a hormone

Answer 66

A

taste, small, sight
stimulate parasympathetic preganglionic neuron (in vagus nerve) to eneteric neurons to stimulate parietal cell, ECL and G cell.
Only a little acid secretion

Answer 67

A

With food in the stomach, get the most acid secretion
Distends stomach, activates neural reflex to stimulate acid secretion
Peptides in food stimulate acid secretion from G cells
Food acts as a buffer to bind hydrogen ions. Lots of hydrogen ions, somatostatin turned on.
- Relieves inhibition

Answer 68

A

Want to limit acid
As food reaches duodenum stimulates factors to feed back inhibits enteric neurons and stimulate enterogastrones
Enterogastrones: hormones that inhibit stomach processes

Answer 69

A

Acetylcholine and histamine directly stimulate parietal cells to increase acid secretion
Gastrin stimulates acid secretion by stimulating histamine release from ECL cells

Answer 70

A

Gastric ulcers (stomach)
Duodenal ulcers
Mucus in the stomach is protective
Use of NSAIDs can block prostaglandin production
- Prostaglandins: promote mucus formation and inhibit acid secretion

Answer 71

A

Causes peptic ulcer disease
Bacteria colonize by burrowing into the mucus and have enzymes that neutralize stomach acid near the bacteria
Causes gastritis (inflammation in the stomach)
Only certain individuals that have H. pylori will have ulcer

Answer 72

A

Gastritis setting up in pylorus
- Causes endocrine deregulation
- Decreased somatostatin, increase in gastrin
- Acid hyper-secretion and no inhibits from somatostain
- Overwhelms protective mechanisms in the duodenum
Gastritis setting up in body
- Atrophy in the glands, decreased parietal cells
- Decreased acid secretion: hypochlorhydria
- Get change in mucosa: intestinal metaplasia: pre-malignant lesion

Answer 73

A

Goal is to eradicate bacteria
Give a couple of antibiotics to really make sure bacteria gone as well as giving drugs to decrease acid secretion
- Histamine antagonists: H-2 receptors, Cimetidine, Ranitidine
- Proton Pump Inhibitors: Omeprazole, Lansoprazole

Answer 74

A

During eating
Expand during ingestion
Neural reflex response to eating

Answer 75

A

Basic propulsive movement
Inside is circular muscle, outside is longitudinal muscle
In segment, two parts: propulsive segment and receptive segment
- Squeeze in propulsive segment and open in receptive segment
  - Contraction in circular muscle and relaxation of longitudinal muscle in propulsive segment
  - Reverse in receptive segment
Stronger peristalsis in pylorus
Once in food pylorus
Rate determined by BER (basic electrical rhythm) (3/min)
Gastric phase stimuli (stomach distension and/or gastrin) increase strength of contractions
Intestinal phase stimuli decrease strength of contractions; slow stomach emptying

Answer 76

A

Rate determined by BER (basic electrical rhythm) (3/min)
Gastric phase stimuli (stomach distension and/or gastrin) increase strength of contractions
Intestinal phase stimuli decrease strength of contractions; slow stomach emptying
Strong contraction in stomach smooth muscle, increase stomach emptying
Weak contraction in stomach smooth muscle, decrease stomach emptying
Enterogastrones: inhibit acid secretion and inhibit smooth muscle
Neural and hormone inputs to GI smooth muscle change the strength, but not the timing of contractions.

Answer 77

A

Providing digestion enzymes and bicarbonate
Exocrine secretion in the pancreas: acinar cells and duct cells
Acinar cells secreting digestive enzymes
Duct cells secreting bicarbonate and fluid
Regulated by hormones
Chyme in duodenum stimulate hormones
- Low pH stimulate secretin release
  - Acts on duct cells to stimulate bicarbonate and fluid release
- Fats and peptides stimulate CCK release
  - Travels in circulation to stimulate secretion from acinar cells
Some stimulation during cephalic and gastric phase via vagus nerve to cause secretions

Answer 78

A

Bile salts, phospholipids, bicarbonate, cholesterol, bile pigments, trace metals. Last three are targeted for excretion
Smooth muscle closing outlet: Sphincter of Oddi
- Basically at the duodenal papilla
- Regulates whether or not bile will enter duodenum
No meal: interdigestive period.
- No need to for bile in duodenum, sphincter contracts
- Pressure builds up and bile flow to gallbladder for storage
Digestive period. About 2 hours
- Sphincter relaxed and bile flows into duodenum
Secretin stimulated by H ions
CCK stimulated by digestive products
- Cholecystokinin
- Cholescyst: gallbladder, kinin: to move
- Triggers smooth muscle contraction in gallbladder
- In SOO relaxes smooth muscle
- Enables bile to flow out
- Amount of bile not sufficient to digest all meal so bile salts need to be recycled…enteroheaptic circulation

Answer 79

A

Transporters take up bile salts in ileum and back to intestinal capillaries

Answer 80

A

Too much cholesterol in gallbladder precipitates to gallstones
- Need enough bile salts to keep it soluable
Female (estrogen promotes cholesterol into bile), age (enzymes producing bile salts less active
- Can be completely asymptomatic

Answer 81

A

When problem is gallstone moved into bile duct.
- Cystic bile duct: painful gallbladder contractions
- Common bile duct: pain and nausea, lack of bile release, failure to excrete bilirubin leads to jaundice
- Duodenal papilla: block pancreatic enzymes leading to inappropriate activation of pancreatic zymogens, acute pancreatitis

Answer 82

A

Cholecystectomy→Removal of gallbladder
Endoscopic removal
Nonsurgical: give oral bile salts
- Delivered to bile ducts via enterohepatic circulation
Shockwaves to break up stones

Answer 83

A

Villus: absorptive
Crypt: secretory enterocytes
- Depends upon activity of CFTR
- Sodium follows chloride passively
Digestive pathologies of cystic fibrosis
- Can cause intestinal blockage
- Pancreatic insufficiency (digestive enzymes not produced/getting to duodenum)
- Chronic pancreatitis
Excessive activation
- Excessive secretion of fluid
- Secretory diarrhea (cholera)

Answer 84

A

Occurs during the digestive period
Turned on by cephalic phase stimuli
Alternating contractions and relaxations of smooth muscle
Helps mix things up
Cephalic phase stimuli switches on segmentationàcontinues during digestive period
Bi-directional movement: things going back and forth
Thing goes forward with gradual propulsion (net movement towards cecum) because BER has gradient: faster in duodenum (12/min) and slower in ileum (9/min)

Answer 85

A

During inter-digestive period
Get segment of pertalsis that travel down upper GI and then stops
Migrating segment of peristaltic activity
Like sweeping floor. Go forward and then backwards, etc.
Clears out what is left in the small intestine
- Indigestible, un-absorbable, bacteria
- Stomach growling: disrupts bubbles
Turns off when eat, because switches to segmentation

Answer 86

A

absorption of fluid
secretion of mucus
bacterial digestion
storage of feces
defecation

Answer 87

A

Slow mixing movement
- Slow irregular contractions of circular muscle
Mass movement
- Propulsive movement
- Sustained contraction of circular muscle (squeeze and hold)
- Provides stimulus for defecation

Answer 88

A

External anal sphincter to maintain continence
Anorectal angle during rest and defection. Contraction of puborectalis establishes more acute anorectal angle that keeps feces from leaking out
- When defecation occur, conscious relaxation to allow feces passage
Mass movement puts feces in sigmoid colon and rectum and causes stretch
- Triggers responses that causes more pressure inside the rectum (see course website)
  - The urge to defecate
- If spinal injury or infants, pressure increases to a point where there is reflective defecation
Valsalva maneuver is pushing to increase abdominal pressure and push feces out
- Contraction of abdominal muscles

Answer 89

A

Hepatic portal vein, deoxygenated put nutrient rich
If water soluble in the diet, then first goes to the liver
Role in nutrient homeostasis
Makes lots of plasma proteins
- Good reason to take amino acids there

Answer 90

A

Cells arranged in rows with sinusoids inbetween
- Place where blood flows through
Look at sinusoid via EM
- In sinusoid are some other cells
  - Enothelial cells
Hepatocytes making bile to go into own distinct secretory pathway
Green guys are canaliculi that hook up to bile ductule to let things flow out of the liver

Answer 91

A

No basement membrane and not tightly linked
Liver secretion and taking things out of blood in sinusoids
- Need lipoproteins to get in and out so need gaps

Answer 92

A

(reticuloendothelial cells)
macrophages; consume aged RBC’s
iron recycling and storage

Answer 93

A

AKA Ito cells
Connective tissue cells
Involved in situation with disorders causing injury to liver cells
Liver can regenerate (with limited capacity)
Chronic Liver injury:
- Stimulates stellate cells
- Can get too much connective tissue…fibrosis
- Can reach terminal stage of fibrosis called cirrhosis
- Connective tissue making islands of isolated hepatocytes that no longer function properly

Answer 94

A

Bile synthesis and secretion
Nutrient homeostasis
- Absorptive state: synthesis of glycogen, TAG
- Post absorptive state: glycogenolysis, gluconeogenesis, ketogenesis
Biotransformation
- Metabolism of drugs, hormones, etc. to promote excretion via the urine
- Convert to more soluble forms
Synthesis of plasma proteins
- albumin, binding proteins, clotting factors, complement
- Albumin is making sure that there is enough osmotic pressure to keep fluid in circulatory system
- When not enough plasma proteins, can get edema
Cholesterol homeostasis

Answer 95

A

Apolipoprotein is also a label for cells to read

Answer 96

A

Are synthesizes in enterocytes from absorbed lipids
Synthesis of TAG in ER

Answer 97

A

TAG rich
Liver makes with extra glucose
Deliver TAG to cells
TAG extracted by lipoprotein lipase, on the surface of endothelial cells and acting of lipoprotein so FA and glycerol can be taken up by cells
When stripped of TAG, becomes more dense and then get taken up by liver and remodeled and sent out as LDL

Answer 98

A

Cholesterol delivery
LDL uptake into cells is via receptor mediated endocytosis
LDL receptor is really important in cell using cholesterol and in liver
Liver using LDL receptor to see how much LDL is out in circulation

Answer 99

A

Cleanup, reverse cholesterol transport
Empty bag that scavenges and picks up extra cholesterol to take back to liver
When high levels of LDL and low HDL cholesterol, increases risk of atherosclerosis
- Fatty plaques inside blood vessels that lead to clots and blockage of blood
Lipid panel measure cholesterol but really we carry about the particles.
Familial hypercholestolemia
- VERY high levels of LDL and have heart attacks at young ages
- Major cause is mutation in gene for LDL receptor
- Defective LDL reecptors means that liver can’t take up LDL and see how much is out there
  - Keeps pumping out LDL

Answer 100

A

synthesis of cholesterol
- HMG-CoA reductase: rate limiting enzyme for cholesterol synthesis; increases cholesterol in the hepatocyte decreases HMG-CoA reductase activity
synthesis of HDL
LDL uptake
- Regulates levels of cholesterol in the circulation
synthesis of bile salts
secretion of cholesterol in bile (some in feces)
- Cholesterol elimination from the body

Answer 101

A

Altered levels of lipids that predispose to atherosclerosis
**statins: ** inhibit HMG-CoA reductase
- Reduce LDL cholesterol
- Shown in clinical trials to reduce cardiovascular events
- May have anti-inflammatory effect
**ezetimibe: **inhibits GI cholesterol uptake
- Blocks cholesterol transporter in the small intestine
Fibrates
Niacin

Answer 102

A

Digestive enzymes released in inactive form
to prevent digesting the cells that create them
Peptide blocks active site of enzyme
Cleave the peptide to activate the enzyme

Answer 103

A

Peptidase in the stomach is pepsin
Active at pH 2-3 and inactive at pH 5
**Chief cells **at the base of gastric glands secrete the zymogen
- called pepsinogen
Partially activation by HCl secreted by parietal cells
Then cleaves the peptide in other pepsinogens to activate them

Answer 104

A

Brushborder enzyme enterokinase cleaves **trypsinogen **forming the active enzyme trypsin
**Trypsin **then activates other enzymes
Pancreatitis
- inapropriate activation
- Acinar cell secrete trypin inhibitor within the pancreas
- Trypsin also has **autolysis **(self-digestion)
Fluid by duct cells flushes zymogens out
- can get blocked by gallstone
Fluid secretion in pancreas depends upon chloride channel CFTR
Increased Risk for pancreatitis
- Mutation in trypsin inhibitor
- Cystic Fibrosis
- Alchol consumption
- hyperlipidemia

Answer 105

A

Most dietary fat is TAG
hydrolyzed by lipase to release FFA and glycerol

Answer 106

A

Key issue in digestion and absorption of fats is their solubility
**lipase **is water soluable and only work at surface of fat droplet
Digestion aided by **emulsifaction **of fat into emulsion droplets
**Bile salts **and cholesterol are ampipathic and are present in the bile
SI motility breaks up fats and then coats them with bile salts and phospholipids to prevent them from sticking together
Digestion occurs in emulsion droplets
- Increases surface area for lipase
Colipase is ampipathic and anchors lipase to surface of emuslion droplet

Answer 107

A

Monoglycerides and glycerol associate with bile salts and phospholipids to form micelles
200 times smaller than emulsion droplets
- small enough to fall between the microvilli
Transport to surface of enterocyte for absorption
Micelle contains **fat soluable vitamins **and cholesterol
Constant forming and breaking down
Only freely dissolved monoglycerides and FFA can be absorbed by diffusion across membrane
Some have facillitate transport proteins

Answer 108

A

Monoglycerides and FA resynthesized back into TAG inside the cell
TAG, cholesterol, fat solubale vitamin packaged into chylomicrons
- are lipoproteins
Released from basal membrane of enterocytes
Enter lacteals and then drained into blood in chest
TAG in chylomicrons is hydrolyzed by **lipoprotein lipase, **found in capillary endothelial cells

Answer 109

A

Some cholesterol in SI is dietary and other is put there by the liver via bile
Only half of cholesterol is absorbed and rest eliminated in the feces
Ezetimibe: blocks transport of cholesterol across apical membrane. Reduced LDL levels, especially when combined with **statins **that inhibit cholesterol synthesis in liver
- Lowers MI and stroke risk as well

Answer 110

A

Iron absorption matches iron loss (1-2 mg)
Iron is necessary component for many enzymes but plays important role in binding oxygen in Hb
- anemia: reduced oxygen carrying capacity of blood
Too much iron can lead to free radical formation
Most iron in RBC, rest in **liver’s hepatoctyes **and Kupffer cells (aka reticuloendothelial cells)
- Macrophage that ingest RBC to release iron
Iron brought into cell by active transporter DMT-1 (divalent metal transporter 1)
- in duodenum
- zinc, copper, cobalt, manganese, cadmium or lead
- also absorb heme iron
Two fates of iron once inside cell:
- leave the enterocyte and enter the body via the basolateral transporter known as ferroportin
- bound to** ferritin, an intracellular iron-binding protein**
  - iron lost when enterocyte dies
Iron in the internal environement is rapidly bound by transferrin
- delivered to RBC precursors and taken up by receptor-mediated endocytosis
Generally more transferrin than iron but, **transferrin saturation **determines if too much iron in the blood (normal 20-45%)

Answer 111

A

One signal reflects the need for iron due to erythropoiesis
- hormone erythropoietin stimulates red blood cell production (another signal for iron absorption)
second signal depends upon the amount of iron in body stores
Regulate iron absorption in the proximal duodenum
** Hepcidin** is produced by hepatocytes when iron stores are full. Inflammation can also stimulate hepcidin production.
- causes ferroportin to be internalized and degraded
- more iron in enterocyte, stimulating ferratin synthesis, more iron loss

Answer 112

A

severe juvenile form of hemochromatosis is due to a homozygous deletion of the gene for hepcidin
HFE functions in the process of sensing body iron levels and regulating hepcidin secretion
deficient secretion of hepcidin, iron absorption by duodenal enterocytes continues even when body iron stores are full
Half a liter of blood contains approximately 200-250 mg of iron

Answer 113

A

also known as** gluten enteropathy** or celiac sprue
malabsorption because of inappropriate immune response to gluten
not atopic becuase not involve IgE
immune response in celiac disease is mediated by CD4+ helper T-cells
All individuals who develop celiac disease express particular alleles of one type of MHC molecule

Answer 114

A

Peptides derived from gluten contain many proline and glutamine residues, making them **resistant to digestion **by pancreatic and brush border enzymes.
peptides gain access to the lamina propria (where MALT is located) either by transcytosis or by a paracellular route
- paracellular by breakdown of tight junctions and increase intestinal permeability
in the lamina propria, an enzyme modifies these peptides, making them even more antigenic
displayed on the surface of antigen presenting cells (APC’s) by MHC II molecules
stimulate CD4+ helper T-cells, which secrete cytokines that orchestrate the inflammatory response that leads to tissue damage
One cytokine in particular (IL-15) stimulates intraepithelial lymphocytes, promoting their recruitment, survival, and cell-killing properties

Answer 115

A

observed in a duodenal biopsy, which is a key test in the diagnosis of celiac disease
flattened mucosa
greatly decreases the surface area of the small intestine, causing** malabsorption of nutrients**, which can cause diarrhea and malnutrition
Duodenal tissue also shows increased numbers of lymphocytes
In adults, primary symptom is **iron deficiency anemia **
get a skin rash, which is termed dermatitis herpetiformis

Answer 116

A

Avoidance
bacterial and plant enzymes capable of digesting the immunostimulatory peptides that resist digestion by human digestive enzymes
block the breakdown in the epithelial barrier of the intestine
- Peptides derived from gluten stimulate the release of** zonulin**, a regulatory molecule that causes tight junctions to open up
- A drug that is in development blocks zonulin receptors

Answer 117

A

often performed** laparascopically**
adjustable gastric banding
- band around fundus
- restrictive procedure because weight loss from limited intake
- More gradual weight loss
RYGB
- both restrictive and malabsorpative

Answer 118

A

CCK, secretin, GLP-1, and GIPact as enterogastrones.

Answer 119

A

Bleeding in the lower GI, left colon
Bleeding from upper GI would cause black, tarry stools
Passage of recognizable blood is called hematochezia
Passage of tarry stools is called melena

Answer 120

A

Descending and sigmoid colon.

Answer 121

A

Infection with Clostridium difficile. Treatment with broad-spectrum antibiotics kills off many bacteria, allowing overgrowth with C. difficile, which causes pseudomembranous colitis.

Answer 122

A

Increased ESR is indicative of inflammation.

Answer 123

A

Ulcerative colitis. Shallow ulcerations that are limited to the mucosa are indicative of ulcerative colitis. Another characteristic feature is the uniform granular appearance seen with colonoscopy.

Answer 124

A

standard treatment to achieve remission is with drugs containing 5-aminosalicylate (5-ASA)

Answer 125

A

Bacteria in the large intestine.

Answer 126

A

If a patient does not achieve remission with a 5-ASA drug, then he might be treated with glucocorticoids. A newer drug for ulcerative colitis treatment is a sort of topical glucocorticoid treatment for the colon. The glucocorticoid drug is contained in a matrix designed to allow steady release once it reaches the colon. This avoids the side effects associated with systemic use of glucocorticoids. More serious cases of inflammatory bowel disease are treated with biologic therapies such as infliximab, a monoclonal antibody drug that inhibits the action of TNF-alpha.

Answer 127

A

Stratified squamous epithelium.

Answer 128

A

The H+/K+-ATPase, or proton pump. Proton pump inhibitors are the most potent antisecretory drugs (drugs that decrease acid secretion).

Answer 129

A

The intestinal epithelium is a simple columnar epithelium. A characteristic feature of intestinal metaplasia is the presence of goblet cells, the mucus-secreting cells that are found in the intestines.

Answer 130

A

cellular abnormalities that indicate the beginnings of malignant transformation leading to cancer.

Answer 131

A

Acid in the stomach kills many bacteria, but H. pylori can evade destruction by burrowing into the protective mucus layer. H. pylori also expresses urease, an enzyme that hydrolyzes urea to produce ammonia, which is used to buffer acid in the immediate environment of the bacterium.
Infection with H. pylori causes chronic** gastritis**, which is inflammation of the stomach lining
Inflammation causes the recruitment of white blood cells and the production of cytokines, which have effects on the physiology of cells in the stomach epithelium

Answer 132

A

excessive quantities of acid
gastritis is localized in the pyloric region
cytokines released in response to inflammation disrupt the regulation of the endocrine cells located in the pylorus
G cells are stimulated to secrete more gastrin, while somatostatin secretion is inhibited
Gastrin stimulates **parietal cell proliferation **and increased parietal cells along with decreased somatostatin leads to acid hypersecretion
acid-neutralizing mechanisms become overwhelmed, and the duodenal tissue becomes damaged.

Answer 133

A

gastritis is located predominantly in the body of the stomach
inflammation induces apoptosis of parietal cells, and there is eventual atrophy of the gastric glands
hyposecretion of acid, or** hypochlorhydria**
Continued tissue damage may lead to development of a gastric ulcer
H. pylori is classified as a carcinogen because infection increases the risk of developing certain types of gastric cancer
atrophic gastric glands undergo a further change known as** intestinal metaplasia**
- begins to resemble an intestinal epithelium, with villi and goblet cells

Answer 134

A

Reducing the acidity in the stomach lumen promotes healing, and it also increases the effectiveness of the antibiotics (for treating H. pylori)
Histamine blockers: these drugs are histamine antagonists that block the stimulatory effect of histamine released by ECL cells
Proton pump inhibitors: these drugs bind to and inactivate the H+/K+-ATPase on the apical membrane of the parietal cell

Answer 135

A

Acinar cells produce digestive enzymes: amylase, lipase, and peptidases
Pancreatic peptidases are produced as inactive zymogens that are only activated after they reach the duodenum
other major secretion is bicarbonate (HCO3-), which is produced by the** duct cells**
- neutralize acidic chyme coming from the stomach
- fluid that is produced by duct cells flushes enzymes and zymogens out into the large pancreatic duct.
intercalated duct
- receive the acinar cell secretions, and secrete bicarbonate and fluid
- connect to larger ducts that eventually lead to the large pancreatic duct that has its outlet at the duodenal papilla

Answer 136

A

small amount of pancreatic secretion occurs due to neural inputs that are triggered by cephalic phase and gastric phase stimuli
majority of pancreatic secretion arises from **intestinal phase stimuli **(when chyme reaches the duodenum)
hormones secretin and cholecystokinin (CCK) are released by endocrine cells that are located in the duodenal epithelium.
secretin release is triggered by H+ ions
- Secretin then travels via the circulation to stimulate bicarbonate secretion by duct cells
CCK release is triggered by digestive products (fats and peptides)
- CCK then travels via the circulation to stimulate secretion by acinar cells.

Answer 137

A

Secretion of bicarbonate by duct cells depends upon the protein** CFTR**
CFTR protein is also a bicarbonate channel
When the CFTR protein is defective, as it is in patients with cystic fibrosis, duct cell secretion is disrupted
- causes a lack of fluid secretion to flush out pancreatic zymogens, blockage of pancreatic ducts, and inappropriate activation of trypsin in the pancreas
damage to acinar and duct cells, which may be replaced by connective tissue
Patients with severe mutations of CFTR (little or no CFTR function) are often born with pancreatic insufficiency, meaning their pancreas does not release sufficient quantities of digestive enzymes
- failure to thrive, and need to be treated with digestive enzyme supplements
Less severe mutations in CFTR (with some channel function) still increase the risk for **pancreatitis. **

Answer 138

A

produced in the liver by hepatocytes
** **contains phospholipids and bile salts, emulsifying agents that are necessary for fat absorption and digestion
bile is also a route for excretion of **cholesterol **and bile pigments
Bile pigments are metabolic breakdown products of hemoglobin and cytochromes that give bile its yellow-green color
Bile pigments are further metabolized by bacteria in the colon, causing feces to have a characteristic brown color
bile contains water and bicarbonate ions that are secreted by duct cells that line the bile ducts within the liver.

Answer 139

A

Whether or not bile is released into the small intestine depends upon the activity of the sphincter of Oddi
interdigestive period, the sphincter of Oddi is contracted, preventing bile from flowing out into the duodenum
pressure increases in the** common bile duct**, and bile flows into the gallbladder
gallbladder, epithelial cells reabsorb water and electrolytes, causing the bile to become more concentrated.

Answer 140

A

During the digestive period, **intestinal phase **signals stimulate the release of bile into the small intestine.
Fatty acids in the lumen of the duodenum stimulate endocrine cells to release the hormone cholecystokinin (CCK)
- stimulates contractions in the smooth muscle of the gallbladder
- causes relaxation of the sphincter of Oddi, allowing bile release into the duodenum.
Acidic chyme in the lumen of the duodenum stimulates other endocrine cells to release the hormone secretin
- Secretin stimulates duct cells in the liver to release bicarbonate into the bile.

Answer 141

A

bile salts present in the body are not sufficient to fully process the fats in a typical meal, thus they need to be recycled
Specific transporters in the terminal ileum move bile salts from the lumen of the digestive tract to the intestinal capillaries
transported directly to the liver via the hepatic portal vein
Hepatocytes take up bile salts from the blood, and increase the secretion of bile salts into the bile canaliculi
95% of the bile that is released to the small intestine is recycled via the enterohepatic circulation,while 5% of the bile salts are lost in the feces

Answer 142

A

maintained by two sphincters that surround the anal canal
internal anal sphincter
- extension of the muscularis externa, and thus is smooth muscle innervated by enteric neurons found in the myenteric plexus
external anal sphincter
- skeletal muscle that can be consciously controlled, and is innervated by somatic efferent neurons
puborectalis muscle
- loops around the rectum like a sling, pulling it forward to create a more acute angle between the rectum and the anal canal
  - anorectal angle
During defecation, there is conscious relaxation of the puborectalis muscle, which creates a more open anorectal angle and allows for a straigther passage through the anal canal

Answer 143

A

mass movement triggers a defecation reflex
- mass movement is a maintained, high-intensity contraction of the circular muscle in the colon, which will propel feces toward the rectum
sufficient volume is deposited in the rectum, the increased pressure will stimulate a reflexive contraction in the sigmoid colon and rectum, relaxation of the internal anal sphincter and contraction of the external anal sphincter
With delay, continued contraction of the external anal sphincter and high pressure eventually trigger reverse peristalsis in the rectum
Defecation involves the relaxation of the external anal sphincter (as well as relaxation of the puborectalis muscle, to create a broader anorectal angle)
Expulsion of Feces
- Valsalva maneuver
- closure of the glottis along with **contraction of abdominal muscles **to increase abdominal pressure

Answer 144

A

in hepatocytes
under** negative feedback regulation**
increased cholesterol in the cell decreases the activity of HMG-CoA reductase
- rate-limiting enzyme in cholesterol synthesis.

Answer 145

A

Two types of lipoproteins are triglyceride-rich: the chylomicrons and VLDL
Chylomicrons are synthesized by enterocytes from lipids absorbed in the small intestine
VLDL is synthesized in the liver
deliver energy-rich triacylglycerol (TAG) to cells in the body
TAG is stripped from chylomicrons and VLDL through the action of lipoprotein lipase
TAG to fatty acids and monoglycerides, which can then diffuse into the cell to be oxidized, or in the case of an adipose cell, to be re-synthesized into TAG and stored in the cell

Answer 146

A

As VLDL particles are stripped of triacylglycerol, they become more dense
deliver cholesterol to cells, where it is used in membranes, or for the synthesis of steroid hormones
Cells take up cholesterol by receptor-mediated endocytosis. LDL binds to a specific** LDL receptor** and is internalized in an endocytic vesicle
Receptors are recycled to the cell surface, while hydrolysis in an endolysosome releases cholesterol for use in the cell

Answer 147

A

Excess cholesterol is eliminated from the body via the liver, which secretes cholesterol in bile or converts it to bile salts
liver removes LDL and other lipoproteins from the circulation by receptor-mediated endocytosis
excess cholesterol from cells is brought back to the liver by HDL in a process known as reverse cholesterol transport
HDL is synthesized and secreted by the liver and small intestine
travels in the circulation where it gathers cholesterol to form mature HDL, which then returns the cholesterol to the liver via various pathways

Answer 148

A

essential nutrient of the vitamin B complex
niacin increases HDL levels and decreases triglyceride and LDL levels
inhibit an enzyme in the liver that is involved in triacylglycerol synthesis, causing a decrease in VLDL production
prolong the half-life of HDL particles by preventing HDL breakdown
Niacin is indicated when HDL is low, as it is the most effective drug for raising HDL levels.

Answer 149

A

bind to the nuclear receptor PPAR-alpha
receptor works as a transcription factor to alter gene expression in target cells
increase HDL levels and decrease triglyceride levels
primarily used when the primary problem is high levels of triglycerides.