Epithelial tissue and blood as a tissue Flashcards
Define the characteristics of epithelia
- Epithelium covers outside and invaginations (gastrointestinal, respiratory, renal and reproductive) to keep fluids in, and infections out
- Most tissues are either epithelium or connective tissue
- Keratin filaments are the cytoskeleton of the epithelial cells
- Have an epithelial embryonic origin
- Epithelial cells are tightly bound together by desmosomes
- Rest on a basement membrane
- Distinct polarity; apical surface has different morphology to the basal surface
- Keratin intermediate filaments
- No vascular supply
- Are constantly renewed by mitosis
What are the roles of epithelium? (5)
- Absorption (small and large intestine) of material at the surface
- Secretion (glands)
- Excretion (tubules of kidneys)
- Gas exchange (lung alveoli)
- Protection (skin)
Describe cell adhesion mechanisms and relate to function and location
- Cell junctions are molecules which ensure cells adhere to the membrane and each other
- Desmosomes very tightly bind cells to each other, although they leave a gap. This gap is to allow water and ions to diffuse passively
- Hemidesmosomes adhere the cells to the basement membrane via keratin filaments
- Tight junctions are a very tight junction, being water and ion impermeable. It has a random criss-cross arrangement within cells. Organs such as bladder and kidney should not absorb urea, hence there are many tight junctions
- Gap junctions are like a channel enabling cell to cell signalling. They are not found in epithelial cells because epithelial cells do not need require action potentials etc. They are found in cardiac cells, neurons and uterus
Identify specialised epithelial cells with unique endocrine and other functions
• Glands are secretory tissues and organs that are derived from epithelial tissues
• Endocrine glands secrete hormones directly into the interstitial fluid and blood stream
• In the small intestine, you’ll find simple columnar epithelium which contains goblet cells. Goblet cells produce mucins which acts as a lubricant
* Respiratory system has pseudostratified columnar epithelium. Here, these epithelial cells have ciliary hairs which enables the movement of mucous out of the respiratory tract
What is the functional definition of a tissue?
Tissues are a group of cells that have a similar structure and act together to perform a specific function
Describe the functions of blood (7)
• Carry O2 and CO2
• Carries nutrients from gut and storage sites to tissues
• Carry waste from tissues to kidneys and liver
• Carry signals throughout body
• Carries drugs
• Carries defensive chemicals to sites of injury
* Maintains osmotic pressure
Identify the cellular constituents of blood (4)
• 55% plasma, 45% cells
• Erythrocytes
• Leukocytes
* Platelets
Describe the process of formation of RBC
- Erythrocytes are made in made in bone marrow
- Start out as pro- erythroblasts
- Manufacture more hemoglobin
- Degradation of organelles
- Expulsion of the nucleus
- Acquisition of final shape
Proerythroblast, basophillic erythroblast, polychromatophillic erythroblast, normoblast, polychromatophillic erythrocyte, erythrocyte
Describe the types of WBC’s
PMN
1. Neutrophilic PMN:
Kill bacteria, Pus formation. It has many granules for phagocytosis and killing of bacteria. They kill by producing oxygen radicals.
2. Basophilic PMN: become mast cells, early response to injury
Eosinophillic PMN
1. Lymphocytes: T cells, B cells etc
Specific immunity, tumour protection. Some may differentiate to plasma cells and make antibodies
2. Monocytes: kill bacteria, eat debris, intracellular pathogens, controls immunity and inflammation. They may emigrate into tissues and become macrophages
Identify the major protein constituents of blood (9)
- Albumin
- Clotting cascade (makes fibrin)
- Fibrinolytic cascade (lyses fibrin)
- Kinin cascade (inflammation and BP regulation)
- Complement cascade (inflammation)
- Anti-bodies/ anti- microbials (specific immunity)
- Transport proteins (solubility and availability)
- Hormones
- Inflammatory mediators
List and describe the function of plasma proteinase cascades
• Coagulation cascade (would make fibrin for stickiness of platelets)
• Fibrinolytic cascade (degrades fibrin to regulate process)
• Complement cascade (inflammation response)
* Kinin cascade (inflammation)
Enzyme cascades
• Phosphorylation/ dephosphorylation cascades (intracellular signalling)
* Caspase cascade (apoptosis)
Outline the process of haemostasis
- Transient arteriolar vasoconstriction:
• The damaged vessels will constrict (vasoconstrict) which reduces the amount of blood flow through the area and limits the amount of blood loss
* This response is triggered by factors such as a direct injury to vascular smooth muscle, chemicals released byendothelial cells and platelets, and reflexes initiated by local pain receptors - Primary haemostasis:
• When the platelets find an exposed area or an injury, they begin to form what is called a platelet plug, aggregating (sticking together) to seal the injury off
• The platelet plug formation is activated by a glycoprotein called the Von Willebrand factor (vWF), which are found beneath the endothelium layer
• They release chemical messengers such as adenosine diphosphate (ADP), serotonin and thromboxane A2 which cause more platelets to stick to the area and release their contents and enhance vascular spasms
• There are a dozen proteins that travel along the blood plasma in an inactive state and are known as clotting factors.
Once the platelet plug has been formed by the platelets, the clotting factors begin creating the Blood Clot - Secondary hemostasis:
• Coagulation or blood clotting uses fibrin threads that act as a glue for the sticky platelets
• As the fibrin mesh begins to form the blood is also transformed from a liquid to a gel like substance through involvement of clotting factors and pro-coagulants
• Once this begins, red and white blood cells become caught up in the fibrin mesh which causes the clot to become even stronger
• The release of Prothrombin also plays an essential part in the coagulation process because it allows for the formation of a thrombus, or clot, to form - Counter- regulatory mechanisms established:
• The endothelium releases tissue plasminogen activators, TPA, (fibrinolytic plasmin) and thrombomodulin (interferes with the coagulation cascade)
* The purpose of this is to prevent inappropriate extension of the haemostatic plug
