Lymphatic, Immune, and GI Flashcards
What are the three major functions of the lymphatic system?
Maintain body fluid level, return fluid from the tissues back to the heart
Helps large molecules like proteins, hormones, and lipids enter the blood
Immune protection and surveillance
What is the lymphatic system composed of?
Lymph, lymphocytes, lymphatic vessels and plexuses, lymph nodes, and other lymphoid organs.
What is the definition of a lymphoid organ? What are examples of lymphoid organs?
Lymphoid organs are the part of the lymphatic system that are directly involved in the immune system because they house or produce lymphocytes and other white blood cells.
Examples of lymphoid organs are the thymus, bone marrow, spleen, lymph nodes, and tonsils.
Which lymphoid organs produce lymphocytes?
The thymus and bone marrow
Which lymphoid organs house lymphocytes and other white blood cells?
The spleen and tonsils
What is lymph and where is it transported?
Lymph is a clear - or slightly yellow - fluid that is transported through tubes like blood vessels, called lymphatic vessels. Lymph fluid enters the extracellular space at capillary beds in the tissues during gas and nutrient exchange.
What is the path of the lymphatic vessels to pick up and transport lymph?
Lymphatic capillaries > lymphatic vessels > lymph nodes > lymphatic trunks > lymphatic ducts
What are the two lymphatic ducts in the body called?
The right lymphatic duct and the thoracic duct
Where does the right lymphatic duct collect lymph from and where does it drain lymph to?
The right lymphatic duct collects the lymph from the right side of the head and neck, the right side of the chest, and the right upper limb
This duct drains its lymph into the right venous angle, the lymph then mixes with blood and drains into the superior vena cava, the lymph then enters the right atrium of the heart
Where does the thoracic duct collect lymph from and where does it drain lymph to?
The thoracic duct collects lymph from the rest of the body not collected by the right lymphatic duct. This includes the left side of the head and neck, the left side of the chest, the left upper limb, the abdomen and both lower limbs.
The thoracic duct travels through the thoracic cavity and drains into the left venous angle. The lymph then mixes with blood and drains into the superior vena cava. The lymph then enters the right atrium of the heart
What are the three major functions of the lymphatic system?
Maintain body fluid level, return fluid from the tissues back to the heart
Helps large molecules like proteins, hormones, and lipids enter the blood
Immune protection and surveillance
What is lymph?
Fluid water and protein in lymph vessels. It is made up of fluid water and protein that seeps out of the capillaries and into the interstitial fluid during gas and nutrient exchange
Is the lymphatic system a closed loop?
No, fluid and proteins make their way into the microscopic lymphatic capillaries, and all the collected lymph is dumped into the veins. Lymph flows one-way only, from the tissues to the heart
Is the circulatory system a closed loop?
Yes, the blood leaves the heart and re-enters the heart through a tightly controlled circuit
Are lymphatic capillaries permeable? Why or why not?
Yes, they are extremely permeable because their walls are made of endothelial cells that only loosely overlap, forming one-way mini-valves. These endothelial cells are anchored to structures in the interstitial space by collagen filaments, which allow the lymphatic capillaries to remain flexible but retain their overall shape
What drives fluid to flow into lymphatic capillaries? Can fluid flow out of lymphatic capillaries and back into the interstitial space? Why or why not?
When the pressure in the interstitial space is greater than the pressure in the lymphatic capillary, the endothelial mini-valves open, allowing fluid to enter.
Fluid cannot flow back out of the lymphatic capillaries into the interstitial space. When the pressure in the interstitial space is less than the pressure in the lymphatic capillary, the endothelial mini-valves are pushed shut, keeping the lymph inside
How does lymph move through the lymphatic system from lymph vessels to trunks?
There’s no central pump pushing the lymph through the lymphatic system. The lymphatic pump is a result of spontaneous contraction of smooth muscle in lymphatic vessels in response to intrinsic and extrinsic factors including increased lymphatic fluid pressure, pulsing of nearby arteries, and the squeezing of skeletal muscles
What prevents lymph from flowing backward in the lymphatic vessels?
The lymphatic vessels have valves just like the veins
What are the two lymphatic ducts in the body called?
The right lymphatic duct and the thoracic duct
Where does the right lymphatic duct collect lymph from?
This duct collects the lymph from the right side of the head and neck, the right side of the chest, and the right upper limb
Where does the right lymphatic duct drain lymph?
This duct drains its lymph into the right venous angle, the lymph then mixes with blood and drains into the superior vena cava, the lymph then enters the right atrium of the heart
Where does the thoracic duct collect lymph from?
This duct collects lymph from the rest of the body not collected by the right lymphatic duct. This includes the left side of the head and neck, the left side of the chest, the left upper limb, the abdomen, and both lower limbs
Where does the thoracic duct drain lymph?
The thoracic duct travels through the thoracic cavity and drains into the left venous angle. The lymph then mixes with blood and drains into the superior vena cava the lymph then enters the right atrium of the heart
What are some key advantages of the lymphatic system over the circulatory system?
It can pick up larger molecules, like hormones, that are too large to get into the capillaries and get them into the bloodstream
The lymphatic system can also help get nutrients to the tissues, specifically chylomicrons, these balls of fat are too large to move across capillaries but can travel in lymphatic vessels and into the thoracic duct then into the venous blood.
What is the lymphatic system’s role in immune function?
Lymphoid organs remove foreign material from the lymph to keep it from entering the bloodstream and act as lookout points for the body’s immune defenses.
What is the definition of a lymphoid organ? What are examples of lymphoid organs?
Lymphoid organs are the part of the lymphatic system that are directly involved in the immune system because they house or produce lymphocytes and other white blood cells.
Examples of lymphoid organs are the thymus, bone marrow, spleen,lymph nodes, and tonsils
How do lymph nodes assist with immune function?
When an infection gets into the tissue, it can slip into a lymphatic capillary and move into a lymphatic vessel which drains into a nearby lymph node where any pathogen or piece of pathogen is detected by a dendritic cell, B cell, or T cell
What are B cells and T cells?
Types of lymphocytes in the lymph nodes that help with the immune response
Dendritic cells sample the lymph and present antigens that they come across to the B cells which produce antibodies that flow into the lymph exiting the lymph node.
T cells are another type of lymphocyte that move between the lymph nodes, lymph, and blood on the lookout for pathogens and infected or abnormal cells that have been tagged by antibodies
Where is the spleen located and are the functions of its two main divisions?
It is a lymphoid organ that sits on the left side of the body below the diaphragm and on top of the stomach.
The spleen has both white pulp and red pulp. The white pulp assists with immune function by generating B cells and the red pulp is where old and defective blood cells are destroyed, and their parts are either broken down or recycled
How does the spleen assist with immune function?
The white pulp of the spleen is where antibody-coated bacteria are filtered out of circulation and antibodies are generated by B cells
Where is the thymus located and when is it most active throughout the lifespan?
The thymus is a lymphoid organ in the upper part of the chest that is most active in the neonatal period and pre-adolescent years, and then slowly atrophies and gets replaced by fat after puberty.
How does the thymus assist with immune function?
The thymus is involved in the development of T cells - making sure that any T cells that react to self-antigens, antigens that are normally found in the body, are promptly destroyed.
How do the tonsils assist with immune function?
The tonsils form a ring of lymphoid tissue around the throat that trap pathogens from ingested food and inhaled air
What is the immune system made of and what is its overall function?
The immune system is made up of organs, tissues, cells, and molecules that all work together to generate an immune response that protects us from microorganisms, removes toxins, and destroys tumor cells
What are the two main types of immune responses?
The innate immune response and the adaptive immune response
How does the innate immune response function in the immune system?
The innate immune response includes cells that are non-specific, meaning that although they distinguish an invader from a human cell, they don’t distinguish one invader from another invader.
The innate response is extremely fast but has no memory so will respond to the same pathogen in the exact same way no matter how many times it sees the pathogen
Are chemical barriers like lysosomes in tears, low pH in the stomach, and physical barriers like epithelium in the skin and gut, and airway cilia part o the innate immune response or adaptive immune response?
The innate immune response
How does the adaptive immune response function in the immune system?
The adaptive immune response is highly specific for each invader. The cells of the adaptive immune response have receptors that differentiate one pathogen from another by their unique parts - called antigens.
The adaptive immune response is specific but slow. The adaptive response relies on cells being primed or activated, so they can fully differentiate into the right kind of fighter to kill that pathogen, and that can take a few weeks
Is adaptive immunity diverse?
Yes, adaptive immunity is diverse, meaning it can recognize almost an infinite number of specific antigens and mount a specific response against each of them
What is immunologic memory and clonal expansion?
Cells that are activated in the adaptive immune response undergo clonal expansion which means that they massively proliferate. Each time the adaptive cells see that same pathogen, they massively proliferate again, resulting in a stronger and faster response each time that pathogen comes around
What happens to clonally expanded cells activated in the adaptive immune response after the pathogen is destroyed?
Once the pathogen is destroyed, most of the clonally expanded cells die off but some of the clonally expanded cells live on as memory cells and they’re ready to expand if the pathogen ever resurfaces
What physiologic structures are the soldiers of the immune system?
The white blood cells or leukocytes
What is hematopoiesis and where does it mainly take place?
Hematopoiesis is the process of forming white blood cells, as well as red blood cells, and platelets and it primarily takes place in the bone marrow
What are the two most common types of white blood cells? What are the other types?
Neutrophils are the most common, followed by lymphocytes.
Other types of WBCs include eosinophils, basophils, and monocytes
How do neutrophils destroy pathogens?
Through phagocytosis, where they get near a pathogen and reach around it with their cytoplasm to “swallow” it whole so that it ends up in a phagosome. Once inside, they use their cytoplasmic granules or an oxidative burst to eliminate the ingested pathogen
What is the role of eosinophils, basophils, and mast cells in the immune response?
They are less common than neutrophils and they contain histamine and other pro inflammatory molecules. They are not phagocytic and are involved in allergic responses. Eosinophils are also known for fighting off parasites. Eosinophils and basophils are WBCs and mast cells live in the tissues
What is the role of monocytes, macrophages, and dendritic cells in the immune response?
They are also phagocytic cells - they gobble up pathogens, present antigens, and release cytokines - which are tiny molecules that attract other immune cells to the area.Dendritic cells are antigen-presenting cells. Dendritic cells are usually found in sites that are in contact with most external antigens - like the skin epithelium, or the gastrointestinal mucosa
Which are found in the blood, monocytes or macrophages?
Monocytes, some monocytes migrate into tissues and differentiate into macrophages, which remain in tissues and aren’t found in the blood
What do dendritic cells do after phagocytosing a pathogen?
Destroy the pathogen and break up its proteins into short amino acid chains. Dendritic cells will then move through the lymph to the nearest lymph node, and they’ll perform an antigen presentation, which is where they present those amino acid chains - which are antigens - to Tcells
What connects the innate and adaptive immune responses?
Antigen presentation is what connects the innate and adaptive immune responses. Antigen presentation is something that can be done by dendritic cells, macrophages, and monocytes
Which cells are referred to as antigen-presenting cells?
Dendritic cells, macrophages, and monocytes
Which of the antigen-presenting cells are best at antigen presenting and why?
Dendritic cells are the best at antigen presentation to T cells because they are the only cells that live where pathogens enter (through epithelia like the skin, gut, and airways) and they are the only cells that can traffic from these tissues to lymph nodes, where Tcells circulate
What is priming specific to the immune responses?
Only T cells with a receptor that can bind to the specific shape of the antigen will be activated
How do T cells recognize an antigen it can bind to?
T cells can only see their antigen if it is presented on a Major Histocompatibility complex molecule (MHC). The antigen-presenting cell will load the antigen on an MHC molecule and display it to T cells, and when the right T cell comes along it binds
What blood cells are lymphocytes? Which are involved in the innate response and which in the adaptive response?
B cells, T cells, and natural killer cells
B and T cells are part of the adaptive immune response and naturalkiller cells are part of the innate immune response
Where are B cells developed?
Bone marrow
Where are T cells developed?
Start in bone marrow then travel to the thymus where they develop into T cells
Where are natural killer cells developed?
Bone marrow
Can lymphocytes travel in blood, tissue, or both?
Both
What is the role of natural killer cells in the immune response?
Natural killer cells are large lymphocytes with granules, they target cells infected with intracellular organisms, like viruses, as well as cells that pose a threat like cancer cells.
Natural killer cells kill their target cells by releasing cytotoxic granules and are involved in the innate immune response.
How are B cells and T cells alike and different in the immune response?
B cells and T cells both have a receptor on their surface that allows them to only bind to an antigen that has a very specific shape.
B cells do not need antigens to be presented to them on an MHC molecule like T cells. They can simply bind to an antigen directly
How do B cells and T cells work together in the adaptive immune response?
When a B cell binds to a protein antigen that’s on the surface of a pathogen, it is capable of internalizing that antigen, degrading it, and presenting it to T cells - so technically, they’re also antigen-presenting cells as well. Like other antigen-presenting cells, the B cell loads the antigen onto an MHC molecule called MHC II and displays it to T cells.
When a T cell gets activated, it helps the B cell mature into a plasma cell, and a plasma cell can secrete lots and lots of antibodies. Typically, it takes a few weeks for antibody levels to peak
What are antibodies?
Antibodies, or immunoglobulins, have the exact same antigen specificity as the B cell they come from
Antibodies are just the B cell receptors in a secreted form, so they can circulate in the plasma, which is the non-cellular part of blood -attaching to pathogens and tagging them for destruction. Because antibodies aren’t bound to cells and float freely in the blood, this is considered humoral immunity
Which cell type is involved in humoral immunity?
B cell antibodies which aren’t bound to cells and float freely in the blood
Which cell type is involved in cell-mediated immunity?
T cells, they are antigen specific, but they cannot secrete their antigen receptor. A naive T cell can be activated or primed to allow it to turn into a mature T cell by any of the antigen-presenting cells, but most often it’s done by a dendritic cell.
What are the two main types of T cells?
CD4 T cells and CD8 T cells - where “CD” stands for cluster of differentiation
What is the function of CD4 T cells?
CD4 T cells are called helper T cells, and they secrete cytokines that help coordinate the efforts of macrophages and B cells.
What is the function of CD8 T cells?
CD8 T cells are called cytotoxic T cells because they kill target cells, like how natural killer cells do it with one major difference. CD8+ Tcells only kill cells that present a specific antigen on an MHC I molecule, whereas natural killer cells aren’t nearly as specific in who they kill
What are cytokines and what are their main functions?
Tiny proteins that are secreted by both immune and non-immune cells to communicate with one another.
What are the main functions of cytokines?
They bind to receptors and trigger a response in the receiving cell.
They promote activation, proliferation, and differentiation of immune cells, but they can also increase the body temperature, causing a fever
What is the difference between autocrine, paracrine, and endocrine signaling in relation to cytokine signaling?
Autocrine means the cell producing the cytokine is also the cell responding to the cytokine.
Paracrine means that the cytokine is produced by one cell and that it affects cells in the near vicinity.
Endocrine, which is when the cytokine affects a cell that’s far away, perhaps in a different organ
What type of signaling do cytokines use?
Mostly autocrine and paracrine but occasionally endocrine
What are the 5 main classes of cytokines?
Interleukins, Tumor Necrosis Factors, Interferons, Transforming Growth Factors, and Colony Stimulating Factors
What is the main function of interleukins?
They are the most varied group of cytokines and are released and act on both leukocytes as well as non-leukocytes.
What is the main function of Tumor Necrosis Factors?
They elicit inflammation and the inflammatory cells. They have a wide variety of biological effects in the inflammatory response, including activating endothelial cells to up regulate the expression of adhesion molecules and increasing vascular permeability
What is the main function of interferons?
They interfere with processes like viral replication
What is the main function of transforming growth factors?
They suppress the proliferation and differentiation of various cells to slow down or stop the overall immune response
What is the main function of colony-stimulating factors?
These cytokines bind to surface receptors on hematopoietic stem cells, causing them to proliferate and differentiate
What are the two main responses of the immune system?
The innate immune response and the adaptive immune response
Put simply, how are the innate and adaptive immune responses different?
The innate response will respond to the same pathogen in the exact same way no matter how many times it sees the pathogen. It is faster than the adaptive response
The adaptive response is highly specific for each invader. It is slower than the innate response
What are examples of chemical and physical barriers associated with the innate immune response?
Chemical barriers- lysozymes in the tears and a low pH in the stomach
Physical barriers- epithelium in the skin and gut, and the cilia lining the airways
How do macrophages, neutrophils, eosinophils, basophils, and mast cells recognize pathogens?
These immune cells have receptors called pattern recognition receptors (PRRs) that recognize the molecules that a pathogen has on its surface called pathogen associated molecular patterns (PAMPs)
What are the key cells of the adaptive immune response?
The lymphocytes- B cells and T cells
As the B cell develops into a plasma cell, what happens to the B cell receptor?
It gets secreted as an antibody with the exact same antigen specificity.These antibody classes are immunoglobulins: IgM, IgD, IgG, IgA, andIgE
What is the integumentary system made of?
Skin and its accessory structures, like oil and sweat glands
What is the integumentary system function?
It protects the body from infections, helps regulate body temperature, and contains nerve receptors that detect pain (nociception), sensation, and pressure.
What are the three layers of skin from the outermost to the innermost layer and what are their functions?
The epidermis is the most superficial layer and it’s responsible for protection from pathogens, the environment, and for vitamin D production
The dermis lies below the epidermis and controls temperature regulation, helps with sensation, and gives the skin its color.
The hypodermis lies below the dermis and provides a point of attachment for the skin to the deeper muscles
What does the dermis layer contain?
It contains nerves and blood vessels
What is hypodermis made of and what is its function?
Hypodermis layer is made of fat and connective tissue that anchors the skin to the underlying muscle
What are keratinocytes?
They are flat pancake-shaped cells that are named for the keratin protein that they’re filled with
What is keratin and what is its function?
It is a fibrous protein that allows keratinocytes to protect themselves from getting destroyed
What is the function of glycolipids?
They help to prevent water from easily seeping into and out ofthe body
Where are melanocytes located and what is secreted by melanocytes?
They are in the stratum basale layer, and they secrete a protein pigment, or coloring substance, called melanin
What is melanin?
Melanin is a broad term that constitutes several types of melanin found in people of differing skin color. These subtypes of melanin range in color from black to reddish yellow and their relative quantity defines a person’s skin color
How does melanin act as a natural sunscreen when keratinocytes are exposed to the sun?
When keratinocytes are exposed to the sun, they send a chemical signal to the melanocytes, which stimulates the melanocytes into making more melanin
The melanocytes move the melanin into small sacs called melanosomes, and these get taken up by newly formed keratinocytes.
Melanin then acts as a natural sunscreen, because its structure dissipates, or scatters, UVB light–which if left unchecked can damage the DNA in the skin cells and lead to skin cancer
How does the epidermis layer help vitamin D production?
Keratinocytes contain cholesterol precursor molecules that are activated by UVB into Vitamin D
What is keratinization?
The process where the keratinocytes flatten out and die, and in the process, they create the epidermal skin barrier
How does the stratum lucidum layer develop and what is it?
Keratinization leads to the development of the stratum lucidum layer which is 2 to 3 cell layers thick of translucent, dead keratinocytes that have secreted most of their lamellar granules
Where can the stratum lucidum layer be found?
The stratum lucidum is only found in thick skin like on the palms and soles of the feet, because those are the areas that need extra protection
What are defensins?
The dead keratinocytes in the stratum corneum layer secrete natural antibiotics called defensins which poke holes in bacteria.
Where is the dermis layer located and is it thicker or thinner than the epidermis layer?
The dermis lies below the stratum basale of the epidermis and it’s much thicker than the epidermis.
What are the two layers within the dermis?
The dermis is divided into two layers - a thin papillary layer below the stratum basale and a deeper reticular layer
What does the papillary layer contain?
The papillary layer contains fibroblasts which produce a connective tissue protein called collagen and macrophages which capture pathogens that make it past the epidermis
What are papillae?
The fibroblasts are arranged in finger-like projections called papillae; each of which contains blood vessels and nerve endings.
What is a Meissner corpuscle and what is its function?
A disk-shaped nerve ending structure that detects fine touch
What are free nerve endings and what is its function?
Dendrites that detect pain (nociception).
What are the similarities and differences between the papillary and reticular layers?
Like the papillary layer, the reticular layer contains fibroblasts with scattered macrophages
But the collagen in the reticular layer is packed very tightly together, making it excellent tissue support.
Fibroblasts in the reticular layer secrete elastin–which is a stretchy protein that gives skin its flexibility.
The reticular layer also contains the skin’s accessory structures like oil and sweat glands, hair follicles, lymphatic vessels, and nerves - and all of the blood vessels that serve these tissues
What is a Pacinian corpuscle and what is its function?
An onion-shaped nerve ending structure that detects pressure or vibration
How does the reticular layer play an important role in temperature regulation?
When body temperature rises, like during a workout, the nervous system makes these blood vessels dilate, and makes the sweat glands secrete sweat.
Dilation of blood vessels brings more blood closer to the skin surface, and that allows heat to get lost to the outside environment.
As sweat coats the skin’s surface, it takes heat to evaporate - so heat is slowly lost from the skin surface with every drop of sweat that evaporates away.
In the opposite situation, when it’s cold outside, blood vessels constrict and that diverts blood flow away from the skin and there’s no sweat -so body heat is conserved.
What does the hypodermis layer contain?
It contains fat cells called adipocytes which help store most of the fat in our body, but also contains fibroblasts, macrophages, blood vessels, nerves, and lymphatics
What are the functions of the hypodermis layer?
It helps insulate deeper tissues, provides padding to the body, and anchors the skin to the muscle with connective tissue proteins like collagen
What structures make up the gastrointestinal (GI) tract?
Mouth, pharynx, esophagus, stomach, small intestine, large intestine, and anal canal
What are the accessory organs of the GI tract?
Teeth, tongue, salivary glands, liver, gallbladder, and pancreas
What are the primary functions of the gastrointestinal system?
Ingestion, digestion, absorption, and excretion
What is the compact ball of food called after it is chewed and lubricated by saliva?
A bolus
What enzyme is contained in saliva to help break long carbohydrates down into smaller sugars?
Salivary amylase
What is peristalsis?
A series of coordinated wave-like smooth muscle contractions in the GItract that help squeeze the food bolus in one direction
What is the function of sphincters in the GI tract?
To prevent food from passing from one part of the GI tract to another
What is the function of the myenteric plexus (AKA Auerbach’s plexus)?
This is a network of nerves that help coordinate muscle contraction and relaxation. When activated, the myenteric plexus causes smooth muscle relaxation
What is the function of the submucous plexus (AKA Meissner’s plexus)?
The submucous plexus is responsible for helping to control the size of the blood vessels as well as the secretion of digestive juices
What is the function of the three cell layers of the intestinal mucosa?
The outermost layer of the mucosa is the muscularis mucosa or muscularis interna, it’s a layer of smooth muscle that contracts and helps break down food.
The middle layer is the lamina propria and it contains blood and lymph vessels.
The innermost epithelial layer, absorbs and secretes mucus and digestive enzymes because this is the layer that comes into direct contact with food
What is the function of the pyloric sphincter (AKA pyloric valve)?
It is a sphincter at the end of the stomach that closes while eating,keeping food inside for the stomach to churn repeatedly
What structure allows the stomach to contract and expand to churn the food?
An extra layer of oblique smooth muscle within the muscularis externa of the stomach
What is the function of gastric glands?
They are found on the inner lining of the stomach and these glands contain a variety of secretory cells which produce gastric secretions
What are gastric secretions made of and what is their function?
Gastric secretions are made up of hydrochloric acid, which help destroy any pathogens that slip through the food, an enzyme called pepsin, which chops up proteins, mucus which protects the stomach, as well as water, which turns the bolus into a liquid pulp, called chyme
What is the food bolus turned into in the stomach with the assistance of gastric secretions?
Chyme
What structure opens to allow chyme to leave the stomach? Where does chyme go when it leaves the stomach?
The pyloric sphincter opens, allowing the chyme to pass from the stomach into the small intestine.
What are the three parts of the small intestine and what is the primary function of the small intestine?
The duodenum, jejunum, and ileum
The small intestine is where most of the digestion and absorption occurs, with the help of the liver’s bile coming from the gallbladder and the pancreatic enzymes.
What is the function of villi and microvilli in the small intestine?
Increase the surface area of the small intestine to absorb nutrients.
What are the accessory organs of the GI system that help with nutrient absorption?
The liver, gallbladder, and pancreas.
What is the function of the liver in nutrient absorption?
The liver is a massive organ that sits under the right dome ofthe diaphragm, and it makes bile which helps to emulsify fats to make them easier to absorb
What is the function of the gallbladder in nutrient absorption?
The gallbladder is the thin-walled, green sac next to the liver, it stores and concentrates the bile that’s made by the liver until it needs to secrete it out into the small intestine to help with fat emulsification
What is the function of the pancreas in nutrient absorption?
The pancreas is a long, skinny gland the length of a dollar bill, next to the duodenum. Hormones from the small intestine stimulate the pancreas to secrete digestive enzymes, water, and bicarbonate that travel through the pancreatic ducts and into the duodenum.
What is the function of cholecystokinin in nutrient absorption?
Fats in the chyme stimulate the hormone-secreting cells of the small intestine to secrete a hormone called cholecystokinin into the blood which goes to the gallbladder and signals it to secrete bile into the small intestine
What is the function of bile in nutrient absorption?
Bile emulsifies the fat, making fat organize into small “micelles”, which are tiny bubbles of mixed lipids and bile acids, rather than clumping together. This makes them easier to absorb
What is the function of the pancreatic lipase enzyme in nutrient absorption?
Pancreatic lipase takes the triglycerides from the micelles created by fats and bile and breaks them down into fatty acids and glycerol
What is the function of the pancreatic amylase enzyme in nutrient absorption?
Pancreatic amylase breaks down carbohydrates into shorter oligosaccharides, and proteases, like trypsin, which cleaves proteins down into smaller peptides
What is the function of the water and bicarbonate released from the pancreas into the small intestine?
To prevent the hydrochloric acid from the stomach from damaging the intestinal mucosa, the small intestine secretes the hormone secretin, which stimulates the pancreatic duct cells to secrete water and bicarbonate.
Bicarbonate helps neutralize the acidic chyme and raising the pH in the intestinal lumen also helps digestive enzymes work more effectively
Other than the pancreas, what other structures secrete bicarbonate into the small intestine?
A generous amount of bicarbonate is also secreted by glands lying inthe submucosa of the duodenal wall.
How are fatty acids and glycerol absorbed in the small intestine?
Fatty acids and glycerol can easily pass through the small intestinal epithelial and into the lymphatics
How are sugars absorbed in the small intestine?
Special enzymes help absorb sugars, on the top surface or brush border of the intestinal cells, called brush border enzymes.
These are maltase, sucrase, and lactase, which break down the short chains of sugars called oligosaccharides into simple sugars, called monosaccharides. These include glucose, fructose, and galactose
How are proteins absorbed in the small intestine?
There are peptidases which break down peptide chains into single amino acids. The epithelial cells can absorb these nutrients into the blood stream, and from there they can go to various tissues around the body
What happens to chyme contents, like fiber, not absorbed in the small intestine?
Whatever isn’t absorbed, like fiber, continues its journey onward through the ileocecal sphincter and into the large intestine (AKA colon).
What are the parts of the large intestine and what is the primary function of the large intestine?
The large intestine is basically a one-and-a-half meter or five-foot-long loop that frames the small intestine.
It consists of six parts: the cecum, appendix, ascending colon, transverse colon, descending colon, sigmoid colon , and finally, the rectum.
The large intestine absorbs excess water from the chyme, and that helps condense it into dry fecal matter
What is the gut microbiome?
Trillions of bacteria that colonize the large intestine, the bacteria help produce essential B and K vitamins, as well as gases like carbon dioxide, methane, and sulfurous compounds
How does the chyme move through the large intestine and what happens a sit moves through?
The chyme slowly moves through the large intestine through small waves of peristalsis that take place over hours or even days
The large intestine absorbs excess water from the chyme, and that helps condense it into dry fecal matter and moves to the rectum
What happens once the rectum is filled and stretched with fecal matter?
Signals travel to parasympathetic neurons in the spinal cord, initiating the defecation reflex. These parasympathetic neurons make the rectum contract and the internal anal sphincter relax.
Meanwhile, signals are sent to the brainstem and thalamus, and when these decide the right moment has come, they allow the external anal sphincter to relax and excrete the feces
What is the path of food from ingestion to excretion?
Mouth
What are the three anatomic divisions of the stomach?
The fundus, body, and antrum
What are the two physiological divisions of the stomach?
The orad region and caudad region
Where does the chyme go once the stomach is done mixing up the chyme?
Duodenum of the small intestine
Where in the stomach do parietal cells secrete hydrochloric acid (HCl) and chief cells secrete pepsinogen?
In the body of the stomach
What happens when pepsinogen is exposed to HCl?
It activates to become pepsin - an enzyme that helps break down proteins
In the antrum of the stomach, there are G cells which secrete a hormone called gastrin into the bloodstream, what is the function of gastrin?
Gastrin increases the HCl secretion of the parietal cells, it increases pepsinogen secretion by the chief cells, and it also increases the contraction of the stomach muscles.
What is the function of the submucosal plexus in the stomach?
It regulates gastric secretions of various glands and controls blood flow to the stomach.
What is the function of muscularis externa layer of the stomach?
It contains three layers of smooth muscle that involuntarily contract in waves called peristalsis, which help the stomach mix, digest and empty the food that it has received
Which region of the stomach has a thicker muscle wall which helps push food towards and past the pyloric sphincter?
The caudad region
What provides the innervation to the three muscular layers of the muscularis externa of the stomach?
The myenteric plexus
What makes up the enteric nervous system?
The myenteric and submucosal plexuses make up the enteric nervous system
How is the enteric nervous system controlled?
It can function without input from the central nervous system and it is connected to the central nervous system, receiving parasympathetic input to increase gastric secretion and motility, and sympathetic input to inhibit those functions
What is receptive relaxation?
When the orad region of the stomach relaxes due to the relaxation of the lower esophageal sphincter
What is the function of the process of retropulsion in the stomach?
It forces chyme in the pylorus to be recycled back to the body of the stomach for more mixing to break food
What does the presence of fat in the stomach do to gastric emptying time?
It increases it
What does the presence of a low pH in the stomach do to gastric emptying time?
It decreases it
What are the general functions of the liver?
Helps to manage the body’s metabolism, detoxification, and bile production
What is the function of the porta hepatis?
The porta hepatis is the gate to the liver and contains the hepatic artery, hepatic portal vein, and the common hepatic duct
What is the function of the hepatic artery?
The hepatic artery delivers oxygen-rich arterial blood from the heart to the liver
What is the function of the hepatic portal vein?
The hepatic portal vein delivers nutrient-rich venous blood from the gastrointestinal tract, but also from the spleen and pancreas
What is the function of the common hepatic duct?
The common hepatic duct drains bile from the liver into the gallbladder
What are the functions of the hepatocytes?
Detoxification, bile synthesis, metabolism of glucose and lipids, synthesis of proteins and lipoproteins, and vitamin and mineral storage
How are hepatocytes involved with detoxification?
As hepatocytes take in oxygen and nutrients and deposit carbon dioxide into the blood, they pick up and detoxify harmful substances like drugs or alcohol
Why is bile synthesis by hepatocytes important?
Bile synthesis is important for the digestion and absorption of fats and fat-soluble vitamins in the small intestine.
How are hepatocytes involved with metabolism?
They are involved with glucose and lipid metabolism, they help maintain a normal blood glucose level by storing glucose as glycogen and breaking down glycogen into glucose and they break down fatty acids to generate ATP, using beta-oxidation
How are hepatocytes involved with protein and lipoprotein synthesis?
Hepatocytes synthesize proteins like albumin and coagulation factors that are important for clot formation. They also synthesize two types of lipoproteins: very low-density lipoproteins or VLDL and high-density lipoproteins or HDL
How do hepatocytes help maintain a normal blood glucose level?
When blood glucose levels are high, hepatocytes convert glucose into a storage molecule called glycogen using a process called glycogenesis
When glucose levels are low, the hepatocytes break down the glycogen back into glucose in a process called glycogenolysis.
What type of lipoproteins do hepatocytes synthesize and what are their functions?
Very low-density lipoproteins or VLDL and high-density lipoproteins or HDL
VLDLs help transport triglycerides, fatty acids, and cholesterol to cells that use them as energy or to adipocytes that store them.
HDLs transport cholesterol from the peripheral cells and tissues back to the liver where they’re broken down to generate energy
Is the liver regenerative?
Yes, you can donate up to 90% of your liver and the remaining 10% can grow it back.
How is bile made?
Hepatocytes convert cholesterol into bile salts which along with water and bilirubin make up bile
Where does bile go after it is synthesized by the liver?
Into small ducts between the hepatocytes then into bile ducts, hepaticducts, cystic ducts, then into the gallbladder
What happens to the bile once it is sent to the gallbladder?
It is stored and becomes more concentrated and is eventually secreted into the small intestine to help with fat absorption
Is the pancreas an endocrine gland, exocrine gland, or both?
It has both endocrine and exocrine functions.
Its endocrine functions are to secrete pancreatic hormones, insulin, and glucagon into the blood to regulate blood sugar levels.
Its exocrine functions are to help neutralize the acidic stomach content and digest food within the intestines
What is the function of the enzyme pancreatic amylase?
It is an enzyme produced by the pancreas which breaks down carbohydrates
What is the function of enzymes trypsin and chymotrypsin?
They are enzymes produced by the pancreas which break down proteins
What is the function of the enzyme lipase?
It is an enzyme produced by the pancreas which breaks down lipids
What do acinar cells and ductal cells of the pancreas each produce? What are each stimulated by?
Acinar cells of the pancreas produce enzymes that help digest food, they are mainly stimulated by cholecystokinin and acetylcholine.
Ductal cells produce aqueous secretions that help neutralize the acidic stomach contents. They are mainly secreted by secretin
Do the concentrations of sodium and potassium in pancreatic secretions fluctuate greatly based on digestion needs?
No, the concentration of sodium and potassium in pancreatic secretions is relatively constant
When does the concentration of bicarbonate in pancreatic secretions increase?
The concentration of bicarbonate increases when there’s a higher demand for acid neutralization.
What is bile and what is its function?
Bile is a greenish liquid that’s made by the liver and is stored in the gallbladder
Bile helps with digestion, absorption of fats, and excretion of various molecules
What is bile made of?
Bile is mainly made up of bile salts and phospholipids, with cholesterol, and bile pigments called bilirubin, making up only a small percentage
Are lipids normally soluble in water?
No, normally, lipids are insoluble in water, that’s why bile is needed to help emulsify and solubilize them
How do bile salts help emulsify lipids?
Bile salts can emulsify large lipid globules into smaller droplets to create a greater surface area upon which pancreatic lipase is able to work to emulsify and help make lipids more soluble
Where is bile produced?
Bile is first manufactured in the liver by cells called hepatocytes.
What is the path of bile from the liver into the gallbladder?
Bile flows into the left and right hepatic ducts which eventually merge to form the common hepatic duct. The common hepatic duct then leads to the cystic duct which brings the bile to the gallbladder
Where is the gallbladder located and what is its function?
The gallbladder is a small pear-shaped hollow organ located beneath the liver, and this is where bile is stored and becomes more concentrated
What stimulates the gallbladder to release bile?
When chyme enters the duodenum of the small intestine it stimulates cells in the lining of the intestine to secrete the hormone cholecystokinin into the bloodstream, once it reaches the gallbladder it causes the release of bile from the gallbladder, into the common bile duct, then into the duodenum
In addition to lipid digestion and absorption, what do bile acids also help with?
With bilirubin excretion
What is bilirubin?
Bilirubin is the pigment that gives bile its color and it’s actually a byproduct of hemoglobin metabolism. Both bile salts and bilirubin can be recycled via enterohepatic circulation where they’re transported from the intestines back to the liver
