Gastrointestinal Hormones and Nutrition

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Questions and Answers

What distinguishes VIP and secretin from other hormones in terms of their classification?

They exclusively influence muscle contraction.

They both belong to the same hormone family. (correct)

They are both derived from the pancreatic cells.

They are only active in the stomach.

Which function is specifically attributed to secretin in the digestive process?

Relaxing the muscles in the gut.

Increasing blood flow to the intestines.

Stimulating the production of gastric acid.

Releasing bicarbonate from the pancreas. (correct)

How do the alpha and beta linkages in polysaccharides differ in terms of digestibility?

Both linkages are indigestible by humans.

Beta linkages have a 'down' orientation making them easy to digest.

Alpha linkages are more resistant to digestive enzymes.

Alpha linkages are easier to digest compared to beta linkages. (correct)

Which statement best describes the coordinated role of VIP and secretin in digestion?

VIP and secretin work together to ensure effective digestive substance release. Signup and view all the answers

Which characteristic is true regarding the structure of amylopectin compared to cellulose?

Cellulose contains beta 1,4 linkages making it indigestible for humans. Signup and view all the answers

What initiates the process that allows the head of myosin to bind to actin in smooth muscle contraction?

Phosphorylation of the myosin light chain by MLCK Signup and view all the answers

Which component directly causes tropomyosin to move away from actin, facilitating muscle contraction?

Calcium binding to caldesmon Signup and view all the answers

What is the role of IP3 in smooth muscle cells?

It stimulates calcium release from the sarcoplasmic reticulum. Signup and view all the answers

Which statement correctly describes the structure and function of unitary smooth muscle?

Only superficial smooth muscle cells are innervated and contract simultaneously. Signup and view all the answers

What occurs immediately after ACh binds to mAChR in smooth muscle cells?

GDP is exchanged for GTP on the alpha subunit. Signup and view all the answers

Which metabolic process primarily occurs in the small intestine?

Absorption of minerals and vitamins Signup and view all the answers

What is the primary structural composition of triglycerides?

Glycerol and fatty acids Signup and view all the answers

What distinguishes phospholipids from triglycerides?

Inclusion of a phosphate group Signup and view all the answers

Which layer of the gastrointestinal tract is primarily responsible for movement and contractions?

Muscularis externa Signup and view all the answers

What role do dense bodies play in smooth muscle cells?

Act as strength junctions between cells Signup and view all the answers

Which component of the gastrointestinal tract is primarily involved in temporary storage of food?

Stomach Signup and view all the answers

What specific type of contraction is peristalsis?

Propulsive contraction Signup and view all the answers

Which of the following is NOT an accessory organ involved in the digestive process?

Stomach Signup and view all the answers

What is an important function of the large intestine?

Form and store feces Signup and view all the answers

Which layer of the tract is responsible for connecting the gastrointestinal organ to the abdominal cavity?

Serosa Signup and view all the answers

What is the primary action of gastrin in the gastrointestinal system?

Stimulates acid production and secretion Signup and view all the answers

CCK is secreted by which type of cell?

I cells in the duodenum Signup and view all the answers

What stimulates the secretion of secretin?

Acidity in the small intestine Signup and view all the answers

Which of the following is a major effect of GIP (Gastric Inhibitory Peptide)?

Induces insulin secretion in a blood glucose-dependent manner Signup and view all the answers

Which hormone is primarily responsible for increasing gastrointestinal motility during fasting?

Motilin Signup and view all the answers

Which type of amino acids primarily stimulates the secretion of cholecystokinin (CCK)?

Aromatic amino acids Signup and view all the answers

What is a minor effect of secretin?

Promotes pancreatic growth Signup and view all the answers

Which hormone decreases appetite as one of its major effects?

GLP-1 Signup and view all the answers

How does GIP affect gastric contractions?

Inhibits gastric contractions Signup and view all the answers

Which of the following statements about CCK is true?

It induces the pancreas to secrete digestive enzymes. Signup and view all the answers

What is the primary action of vasoactive intestinal peptide (VIP) when released by inhibitory motor neurons?

Promotes muscle relaxation Signup and view all the answers

Which neurotransmitter is the major excitatory factor that increases the likelihood of gastrointestinal contraction?

Acetylcholine Signup and view all the answers

What component is essential for the functioning of interstitial cells of Cajal (ICCs) in the GI tract?

Kit gene Signup and view all the answers

What is the primary function of guanylyl cyclase when stimulated by nitric oxide (NO) in the gastrointestinal tract?

Convert GTP to cGMP Signup and view all the answers

Which type of efferent neuron is responsible for stimulating smooth muscle contraction in the enteric nervous system?

Enteric motor neurons Signup and view all the answers

How does the sympathetic nervous system primarily affect gastrointestinal smooth muscle?

Inhibits smooth muscle activity Signup and view all the answers

What is a key feature of the electrical slow waves generated by the interstitial cells of Cajal?

They are synchronized between different GI regions. Signup and view all the answers

What type of signaling involves a hormone acting on itself?

Autocrine signaling Signup and view all the answers

Which type of receptor is primarily involved in hormone signaling as described in the content?

G protein coupled receptors Signup and view all the answers

Which neurotransmitter is primarily released by enteric neurons to promote vasodilation in the GI tract?

Nitric oxide Signup and view all the answers

How does the enteric nervous system relate to the autonomic nervous system?

It operates separately but integrates inputs from both SNS and PNS. Signup and view all the answers

What determines the different contraction rates in various parts of the GI tract?

Intrinsic pacemaker activity Signup and view all the answers

Which hormone is NOT mentioned as influencing the GI tract's function?

Cortisol Signup and view all the answers

Study Notes

VIP and Secretin

VIP (Vasoactive Intestinal Peptide) and secretin are members of the same hormone family.
They are both crucial for regulating digestive processes.
VIP promotes muscle relaxation in the gut, blood flow to the intestines, and digestive juice release.
Secretin triggers the pancreas to release bicarbonate, which neutralizes stomach acid, making the environment in the intestines more optimal for digestion.

Macronutrients & Absorbable Units

Carbohydrates (polysaccharides, disaccharides) are broken down into glucose, fructose, and galactose.
Proteins are broken down into amino acids.
Fats (triglycerides, phospholipids, cholesterol esters) are broken down into glycerol and fatty acids.

Brief Anatomy of the Gastrointestinal Tract

The GI tract is essentially a long, continuous tube with attached accessory organs.
The tube consists of the oral cavity, esophagus, stomach, small intestine, and large intestine.
Accessory organs include the salivary glands, pancreas, and biliary system (liver, gallbladder, and associated tubes).

Layers of the Tract

Four main layers: serosa, muscularis externa, submucosa, and mucosa.
Serosa: outermost layer, responsible for connecting the GI organ to the abdominal cavity.
Muscularis Externa: contains smooth muscle responsible for contractions, including peristalsis (propulsive) and segmentation (mixing).
Submucosa: connective tissue, lymphatic vessels, and blood vessels are found here.
Mucosa: innermost layer.

Smooth Muscle Cells (SMC)

Small, single-nucleated cells that are important for contractions and muscle movement.
They are organized in a network with dense bodies, collagen fibers, and actin and myosin filaments.
Ca2+ influx is critical for contraction, and the process involves "moving" tropomyosin out of the way allowing myosin heads to bind to actin filaments.
Phosphorylation of the myosin light chain (tail) is crucial for cross-bridge formation and the powerstroke.

Regulation of Smooth Muscle Contraction

Excitatory: Acetylcholine (ACh) is a primary excitatory neurotransmitter that activates the PLC-B pathway, resulting in IP3 production, Ca2+ influx, and contraction.
Inhibitory: VIP and norepinephrine (released by the SNS) work through G-protein coupled receptors to inhibit contraction by blocking Ca2+ influx, opening K+ channels (hyperpolarization), and preventing MLCK activation.

Pacemaking in the GI Tract

The GI tract exhibits rhythmic contractions, with different regions having different rates.
Interstitial cells of Cajal (ICCs) act as pacemaker cells, generating slow waves of electrical activity that regulate contraction patterns.

Neuronal Control of the Tract

Intrinsic: The enteric nervous system (ENS) is the "brain of the gut" and is responsible for integrating and coordinating various digestive processes.
Extrinsic: The autonomic nervous system influences the GI tract via the sympathetic (SNS) and parasympathetic (PNS) branches.
Sensory: Sensory neurons (both spinal and vagal) detect stimuli in the lumen, wall, and muscle, and send this information to the CNS for processing and response.

Enteric Nervous System (ENS)

Contains neurons, axons, and cell bodies entirely within the GI tract.
Efferent: Motor neurons control contractions, secretomotor neurons stimulate exocrine secretions, endocrine neurons release hormones, and vasodilator neurons regulate blood flow.
Afferent: Sensory neurons (IPANS) detect various stimuli including chemicals and mechanical changes.
Interneurons: Integrate information from afferents and regulate enteric efferents.

Endocrine Control of the Tract

The GI tract produces numerous hormones that regulate a variety of processes.
Gastrin: Produced by G cells, primarily stimulates gastric acid secretion.
Cholecystokinin (CCK): Released by I cells, stimulates pancreatic enzyme secretion, gallbladder contraction, and bicarbonate production.
Secretin: Produced by S cells, induces bicarbonate production and secretion by the pancreas and biliary system.
Gastric Inhibitory Peptide (GIP): Released by K cells, inhibits gastric contractions and secretion and stimulates insulin release.
Motilin: Produced by M cells, increases GI motility during fasting.
GLP-1: Released by L cells, stimulates insulin release by the pancreas, decreases gastric emptying, and reduces appetite.
Other: Epinephrine, growth hormone, and insulin also influence GI function.

Hormone Signaling Mechanisms

Endocrine: Hormones travel through the bloodstream to target cells.
Paracrine: Hormones act on nearby cells via the extracellular fluid (ECF).
Autocrine: Hormones act on the same cell that released them.

Hormone Receptors

G protein-coupled receptors: Hormone binding activates the alpha subunit, which then initiates a signaling cascade.
Receptor-linked enzymes: Hormone binding activates enzymatic activity within the receptor, triggering downstream signaling events.

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Description

This quiz covers the functions of specific hormones like VIP and secretin that regulate digestion, as well as the breakdown of macronutrients into absorbable units. You'll also learn about the anatomy of the gastrointestinal tract and its accessory organs. Test your understanding of these essential biological processes!