L24 - Animal Digestion
Learning Objectives:
Be able to describe what digestion is and why it’s essential in animals
Questions:
What are the three needs that satisfy an adequate diet?
Chemical energy for cellular processes
Organic building blocks for macromolecules
Essential nutrients → Required materials an animal requires but can’t assemble
Amino acids, fatty acids, vitamins, minerals
How many amino acids do organisms require? What is an essential amino acid? How does this relate to animals?
All organisms require 20 amino acids, and plants and microorganisms can normally produce all 20
Essential amino acid → one that cannot be synthesized by cellular biochemical pathways and instead must be ingested
Most animals can synthesize around half of their amino acids
Humans are unable to synthesize 8/20 of the amino acids, and have to obtain in our diets
What is the link to cellular respiration?
See figure
Be able to describe the general structure and organization of a mammalian digestive tract
Questions:
How can animals extract the nutrients they need from food while not digesting their own tissues?
Compartmentalized processing protects body tissues while allowing enzymes and acids to break down nutrients
What are the stages of food processing?
Ingestion → mechanical digestion
Food is isolated in a specialized organelle or compartment to be broken down chemically without damage to other cellular areas
Digestion → chemical digestion (enzymatic hydrolysis)
Extracellular process where food is isolated and broken down outside a cell in a body compartment
Absorption → nutrient molecules enter body cells
Breakdown products ar taken up into the bloodstream
Elimination → undigested material
Material is eliminated out of the digestive system
How are digestive tracts organized/divided?
How is the human digestive system formatted?
Composed of a central digestive tract and associated accessory glands
Digestive tract is not passive tube, but secretes enzymes and other chemical compounds, absorbs nutrients, and actively moves food through body via peristalsis
What is the anatomy of the digestive tract?
Made up of several layers of tissue (each w specialized function)
Lumen → central space where gut contents travel
Mucosa → inner tissue layer w secretory and absorptive functions
Submucosa → surrounds mucosa; layer containing blood vessels, lymph vessels, and nerves
Be able to describe major digestive events that happens as food passes through the digestive tract
Questions:
What are the processes of digestion in the stomach?
Stores food and processes it into a liquid suspension
Mechanical digestion → peristaltic contractions churn bolus
What is the process of chemical digestion in the small intestine?
Food enters small intestine
Protein and carb digestion continue
Fat digestion begins
Carried out by the small intestine along with pancreas and liver
Liver produces bile → aids in fat digestion by breaking large clusters of fats into smaller lipid droplets (emulsification)
Bile produced by the liver is stored in the gallbladder
How does absorption work in the small intestine?
Large surface area → villi and microvilli exposed to intestinal lumen
Transport across the epithelial cells → passive/active depending on nutrient
Hepatic portal vein → carries nutrient–rich blood from the villi capillaries to the liver and then to heart
How are nutrient molecules like glucose absorbed in the intestine?
Glucose and amino acids are cotransported with sodium ions into intestinal cells
Sodium ions bind to transmembrane proteins that also bind nutrient molecules
The movement of sodium down its concentration gradient drives nutrient absorption into the cell
How does absorption occur in the large intestine?
Absorption of Na+ and Cl– ions creates an osmotic gradient across large intestinal mucosa
Drives passive water absorption
Water and electrolytes are primarily absorbed in the proximal colon
Water absorption is passive and driven by solute transport
Water intake and secretion balanced with absorption
What does your digestive system do in a day?
Your digestive tract is continually functioning with the inflow (secretion) od substances and outflow (absorption) of substances
What is a good example of symbiosis within the digestive tract?
Relationship of gut bacteria (E. coli) and their animal host:
Bacteria aid in digesting nutrients the host cannot extract on its own
Bacteria obtain nourishment from the host’s gut contents
Bacteria produce essential nutrients and vitamins like biotin and vitamin K
The relationship benefits both the bacteria and host, supporting a healthy microbiome
How does the gut microbiome impact human health?
The gut microbiota functions as a vital organ with connections to other body systems
Forms a multidirectional communication axis with other organs
Imbalances in the gut microbiota (dysbiosis) are linked to various diseases, including:
Anxiety and depression
Hypertension and cardiovascular diseases
Obesity and diabetes
Inflammatory bowel disease
Cancer
Vocabulary:
Essential nutrients
Required materials an animal requires but can’t assemble
(i.e. amino acid, fatty acids, vitamins, minerals)
Essential amino acid
One that cannot be synthesized by cellular biochemical pathways and instead must be ingested
Digestion
Food is isolated and broken down outside a cell in a body compartment
Absorption
Following digestion, the breakdown products that are taken up into the bloodstream
Peristalsis
involuntary contraction and relaxation of longitudinal and circular muscles throughout the digestive tract
Lumen
central space where gut contents travel
Mucosa
inner tissue layer w secretory and absorptive functions
Submucosa
surrounds mucosa; layer containing blood vessels, lymph vessels, and nerves
Emulsification
the process of breaking down large fat globules into smaller, uniformly distributed droplets
Hepatic portal vein
The vein that carries nutrient-rich blood from the villi capillaries to the liver, then to the heart
Dysbiosis (of the gut)
an imbalance of microorganisms in the intestines, specifically a shift away from a healthy microbial community towards an unhealthy one