Lecture 22- Digestion Flashcards
What type of organisms must ingest food?
Heterotrophs- must ingest food, cannot fix carbon
What are the 4 stages of food processing?
- Ingestion
- Digestion
- Absorption
- Elimination
Ingestion (basic)
Food-> digestive cavity
Digestion (basic)
Macromolecules -> monomers- can be absorbed
Mechanical, chemical
Absorption (basic)
Cells take up small molecules
Elimination (basic)
Undigested material passed out of digestive system
Location of Digestion. Enzymes hydrolyze tissue- how do you digest food without digesting yourself?
2 methods- Intracellular digestion and extracellular digestion
Intracellular digestion- food vacuoles fuse with lysosomes
Extracellular digestione- digestion in extracellular component
Continuous with outside of body
Peristalsis
Waves of contractions in smooth muscle
Moves food
Sphincters
Ring-like, muscular valves (circular muscles)
Regulate passage between compartments
Before Ingestion
Digestive process triggered in NS
Stimulation of salivary glands
Food Processing prior to Stomach in Oral cavity
Oral cavity (mouth)- Ingestion, early digestion
Mechanical- teeth
Chemical- salivary amylase
Starch, glycogen-> smaller polysaccharides, maltose
Mucus- contains mucins- slippery glycoproteins
Tongue- moves food, forms bolus
Pharynx
Passage to digestive and respiratory systems
Swallowing: Bolus-> esophageal sphincter-> esophagus
Esophagus
Muscular tube connecting pharynx-> stomach
Bolus-> stomach via peristalsis
Cardiac sphincter: Junction with stomach
Controlled by smooth muscle ring
Cardiac Sphincter
Junction with stomach
Controlled by smooth muscle ring
Stomach
Highly elastic, 2L capacity
Can store meal, don’t need to eat constantly
Lining replaced every 3 days
Mechanical Breakdown
As you chew, your teeth break down the food into smaller pieces, increasing surface area for better enzyme action.
Chemical Breakdown
Throughout chewing, salivary glands located around the mouth secrete saliva.
What do saliva contain?
Salivary amylase and mucus
Function of salivary amylase
Breaks down starch and glycogen into smaller polysaccharides like maltose.
Function of mucus
This lubricating substance contains muffins- slippery glycoproteins- that coat the food particles, making swallowing easier and protecting the mouth lining from irritation.
Function of tongue
The tongue moves food around, ensuring thorough mixing with saliva and facilitating grinding by the teeth.
Bolus formation: The tongue shapes and compacts the chewed food particles (along with saliva) into a moistened mass called a bolus.
Passage of the bolus after ingestion through oral cavity (Oral cavity-stomach)
During swallowing, the bolus moves from the mouth to the pharynx which is the passage to both digestive and respiratory systems. The bolus goes to the esophageal sphincter, which is a muscular ring that relaxes to allow the bolus to pass through to the esophagus. The bolus is then propelled down the esophagus, a muscular tube connecting the pharynx to the stomach, by a wave-like motion called peristalsis. This involuntary muscle contraction helps move the food down the esophagus. The cardiac sphincter is the junction with the stomach controlled by smooth muscle ring that opens and allows the bolus to enter the stomach.
Stomach Lining
Has many pits- tubular gastric glands
These glands produce and secrete gastric juices.
What are the three types of gastric juices produced by the tubular gastric glands in the stomach lining?
Mucuous cells, chief cells, parietal cells.
What is the function of mucous cells in the stomach lining?
Secrete mucus.
Mucus serves a protective role. It coats the stomach lining, shielding it from the harsh acidic environment created by the parietal cells.
What is the function of chief cells in the stomach lining?
Secrete pepsinogen-inactive precursor of pepsin.
These cells produce an inactive enzyme called pepsinogen. Pepsinogen isn’t an active enzyme. It needs a slightly acidic environment for activation. Once activated by the acidic environment created by the parietal cells, pepsinogen becomes pepsin, the stomach’s primary digestive enzyme. Pepsin breaks down proteins in food into smaller peptides.
What is the function of parietal cells in the stomach lining?
Pump H+ into lumen, Cl- diffuses out-> HCl
These cells have a special pump that actively pumps H+ into the stomach lumen from the bloodstream. As H+ ions are pumped in, Cl- passively diffuses out of the parietal cells to maintain electrical neutrality. This creates a high concentration of H+ ions in the stomach lumen, resulting in the formation of hydrochloric acid (HCl).
Function of HCl
Creates a highly acidic environment in the stomach (pH ~2) to kill or inhibit growth of bacteria in food.
Denatures proteins (more accessible to digestive enzymes)
Converts pepsinogen-> pepsin: Main digestive enzyme.
(Once pepsin is activated, it acts as an endopeptidase. This means it can break down proteins into smaller polypeptides.
What is an endopeptidase?
When pepsinogen is converted into pepsin by HCl, it becomes the main digestive enzyme. Pepsin acts as an endopeptidase, meaning that it breaks down proteins into smaller polypeptides.
What are the three steps associated with the production of gastric juice?
- Pepsinogen and HCl secreted into lumen.
- HCl converts pepsinogen to pepsin.
- Pepsin activates more pepsinogen, starting a chain reaction.
What is chyme composed of?
End product when leaving stomach. Consistency of thick soup, pH ~2.
Mixture of…
- Partially digested carbs
- Small polypeptides
- Undigested material
Where does chyme leave from and go to?
Exits from stomach-> pyloric sphincter-> small intestine
What are the three divisions of the small intestine?
~6m long, “small” diameter
3 divisions
Duodenum: Where most chemical digestion occurs
Jejunum: Between duodenum, ileum
Ileum: Lower portion
Process of food through oral cavity- stomach
Mechanical + chemical breakdown in oral cavity
Tongue forms bolus
Bolus moves from the mouth to the pharynx (passage to digestive and respiratory systems)
Bolus goes to the esophageal sphincter, which is a muscular ring that relaxes to allow the bolus to pass through to the esophagus. The bolus is then propelled down the esophagus, a muscular tube connecting the pharynx to the stomach, by a wave-like motion called peristalsis. This involuntary muscle contraction helps move the food down the esophagus. The cardiac sphincter is the junction with the stomach controlled by smooth muscle ring that opens and allows the bolus to enter the stomach.
What is the function of HCl?
Makes a highly acidic environment (pH of stomach ~2)
Acts as an antimicrobial- kills bacteria in food, helps prevent food borne illness.
Denatures proteins, making them more accessible to enzymes.
Activates pepsin, the main protein digesting enzyme.
Allows pepsin to break down proteins into smaller polypeptides.
Once activated, pepsin acts as what?
An endopeptidase. This means it can break down proteins into smaller polypeptides.
What is chyme?
Consistency of thick soup, pH ~2
Mixture of…
- Partially digested carbs
- Small polypeptides
- Undigested material
Where does chyme go when it leaves the stomach?
Stomach-> pyloric sphincter-> small intestine
What are the 3 divisions of the small intestine?
~6m long, “small” diameter
3 divisions
Duodenum: Where most chemical digestion occurs
Jejunum: Between duodenum, ileum
Ileum: Lower portion
Digestion of Carbohydrates- what are they broken down into, where are they broken down, and what breaks them down
Carbohydrates- poly, disaccharides-> monosaccharides
Oral cavity- salivary amylase
Small intestine- pancreatic amylase, disaccharidases
Think -amylase, -ridase
Digestion of Proteins- what are they broken down into, where are they broken down, and what breaks them down
Polypeptides-> amino acids
In stomach: Pepsin
In small intestine: Pancreatic trypsin, chymotrypsin, dipeptidases, carboxypeptidases, aminopeptidases
Think -trypsin and -peptidase
Digestion of Nucleic Acids- what are they broken down into, where are they broken down, and what breaks them down
DNA, RNA-> nitrogenous bases, sugars, phosphates
In small intestine:
Pancreatic nucleases
Nucleotidases
Nucleosidases
Phosphatases
It fits. Nucleo-. And Phosphate.
Digestion of Lipids- what are they broken down into, where are they broken down, and what breaks them down
Usually ingested as large masses of triacylglycerols (triglycerides)
Hydrophobic- problem- enzymes water soluble
In small intestine:
Bile salts from liver emulsify
Increased surface area, breaking down fats into smaller pieces.
Now, pancreatic lipases -> glycerol, fatty acids, monoglycerides
Absorption in Small Intestine
Absorption via villi and microvilli
Each villus contains
- Capillaries
- Lacteal
Transport Processes during absorption
How are…
- Glucose/amino acids
- Fructose
- H2O
- Ions
Transported?
Glucose/amino acids- combination of facilitated diffusion and active transport
Fructose- facilitated diffusion
H2O- simple diffusion
Ions- active transport
What is the process of lipid absorption?
Lipid absorption is more complicated because they are hydrophobic. The free fatty acids and monoglycerides enter the villus via diffusion. Inside the villus, the lipids are reformed into triglycerides and packaged as chylomicrons. They then enter the lacteal in the villus, which helps them travel through the lymph to the bloodstream.
What’s left after absorption in the small intestine?
Most nutrients absorbed
Undigested protein, fats, carbs
Indigestible material- cellulose, dead cells
All enter large intestine
What are the 4 divisions of the large intestine?
Ascending
Transverse
Descending
Sigmoid
Larger diameter
Entry regulated by ileocecal valve
Absorption and Elimination in LI
Mostly water recovery
Many bacteria present
Beneficial- Produce vitamins, outcompete pathogens
Feces eliminated- digestive waste, not involved in metabolism- ~75% H2O, 25% solid
Large intestine-> anus
Where is the liver located? What is transported to it?
Located between heart and stomach/SI
Capillaries from SI converge into veins-> hepatic portal vein
Transports blood to liver
Functions of liver
- Excess glucose removed from blood and stored as glycogen
- Nutrients converted (Synthesize proteins, excess calories-> fat)
- Modify, detoxify alcohol and other drugs
What is the primary function of pepsin?
Breaks down proteins into smaller polypeptides
Where are bile salts synthesized?
Liver
A(n)__________ is a circular muscle that controls the passage of matter between orifices in animals.
Sphincter
What do the salivary glands secrete?
Salivary amylase and mucins
Where does digestion occur in large multicellular organisms?
Alimentary canal
In what regions of the body are carbohydrates digested?
Oral cavity and small intestine
What is the main purpose of mechanical digestion?
Break down large pieces of food into smaller pieces which increases the surface area for enzymes to work upon.
What physiological process occurs during pre-ingestion?
Salivary secretion
________ are microscopic cellular membrane protrusions that increase the surface area of the small intestines.
Microvilli
True or False: The primary function of the stomach is the digestion of carbohydrates.
FALSE. The primary function of the stomach is the digestion of proteins.
What do the mucus cells in the stomach secrete and what is the function of the secretion?
Mucus- protects tissues from acid
What is the primary function of bile salts?
Adhere to fats and emulsify them.
Which organs/glands are considered accessory exocrine glands for digestion?
Salivary glands / Pancreas / Gallbladder / Liver
What function does the tongue have during digestion?
Formation of a food bolus
In what regions of the body are proteins digested?
Stomach & Small intestine
Which enzymes aid in carbohydrate digestion in the small intestine?
Pancreatic amylase & Disaccharidases (lactase)
The pharynx and the stomach are connected by a muscular tube known as the _____.
Esophagus
The large intestine is responsible for the absorption of _____.
Water
Where does the majority of nutrient absorption occur?
Small intestine
_____ is the semi-fluid mass of partly digested food that is expelled by a person’s stomach, through the pyloric valve, into the duodenum.
Chyme
Where does digestion occur in single-celled organisms?
Food vacuoles / Lysosomes (intracellular digestion)
What do the parietal cells in the stomach secrete and what is the function of the secretion?
Hydrochloric acid (HCl) - antimicrobial
The _____ controls the passage of food from the junction between the esophagus and the stomach.
Cardiac sphincter
A(n) _____ is a lymphatic capillary that absorbs dietary fats in the villi of the small intestine.
Lacteal
Which enzymes are secreted by the small intestines to aid in nucleic acid digestion?
Nucleosidases / Phosphatases
True or False: Monoglycerides and fatty acids use simple diffusion to travel across the intestinal epithelium.
TRUE
What are mucins and what is their function?
Glycoproteins which aid in lubrication during ingestion
What is peristalsis?
Process by which smooth muscle contraction and relaxation propagates waves
What do chief cells in the stomach secrete?
Pepsinogen
A food bolus travels from the oral cavity to the _____ after swallowing.
Pharynx
Gastric chief cells work in conjunction with parietal cells to convert pepsinogen to _____.
Pepsin
The _____ is a blood vessel that carries blood from the gastrointestinal tract, gallbladder, pancreas, and spleen to the liver.
Hepatic portal vein
The _____ connects the stomach to the duodenum.
Pyloric sphincter
Which enzymes are secreted by the small intestines to aid in protein digestion?
Dipeptidases / Carboxypeptidases / Aminopeptidases
Where are nucleic acids digested?
Small intestine
What happens to monoglycerides and fatty acids after they travel into the intestinal epithelium?
Reassembled into triglycerides and packaged into chylomicrons
What are the three regions of the small intestines?
Duodenum → Jejunum → Ileum
Lipids are ingested as _____.
Triglycerides (triacylglycerol)
Which pancreatic enzyme is secreted into the small intestine to aid in lipid digestion?
Pancreatic lipase
What do the bacteria in the large intestine produce?
Vitamins, outcompete pathogens
In which region of the small intestine does most digestion occur?
Duodenum
Which pancreatic enzymes are secreted into the small intestine to aid in protein digestion?
Trypsin & chymotrypsin
Which pancreatic enzymes are secreted into the small intestine to aid in nucleic acid digestion?
Pancreatic nucleases
What are chylomicrons (ULDL) and what is their function?
Lipoprotein particles that transport dietary lipids from the intestines to the lacteal
The _____ is a sphincter muscle that separates the small intestine and the large intestine.
Ileocecal valve
True or False: The large intestine is longer than the small intestine.
False; the large intestine is shorter but larger in diameter
True or False: The majority of protein disgestion occurs in the large intestine.
False; digestion is completed in the small intestine
What are feces composed of?
75% water / 25% solids
Sequence the pathway of matter through the large intestine.
Ascending colon → Transverse colon → Descending colon → Sigmoid colon → Rectum
What are the primary functions of the liver?
Alcohol/drug/poison detoxification / Synthesis of bile / Glycogenesis
