1
Q
Tunica Intima Layers
A
- Endothelium
- Basal Lamina
- Subendothelial CT
- Internal elastic lamina
- Composed of elastin
- Fenestrated
- Seperates intima from media in arteries
- Most prominant in muscular arteries
2
Q
Tunica Media
A
- Usually the thickest layer in arteries
- Contains circularly arranged smooth muscle
- Contraction narrows lumen
- Contains elastic fibers, reticular fibers, & proteoglycans
- All produced by smooth muscle cells
- In capillaries and post-capillary venules, layer is replaced by pericytes
- External elastic lamina
- Seperates media from adventitia
- Most prominent in muscular arteries
- Fenestrated
3
Q
Tunica Adventitia
A
- Longitudinally oriented collagen and elastic fibers
- Primarily type I collagen
- Blends into surrounding CT
- Contains autonomic nerves that enter tunia media and innervate smooth muscle
- In thick vessels, contains small blood vessels called vasa vasorum
- Nourish adventitia & media of vessels too thick for diffusion
- More frequent in veins than arteries
4
Q
Vasculature Innervation
A
- Smooth muscle in tunica media of most organs innervated by sympathetic fibers that release norepinephrine
- Causes sympathetic vasoconstriction response
- More prevalent in arteries than veins
- Most common in skin and kidneys
- Skeletal muscle blood vessels innervated by sympathetic fibers that release acetylcholine
- Causes sympathetic vasodilator response
- Parasympathetic fibers innervate very few organs
- Salivary glands
- Erectile tissue of penis
- Release acetylcholine, nitric oxide, and other co-transmitters
- Causes parasympathetic vasodilator response
5
Q
Endothelial Cell
Functions
A
- Permeability barrier
- Secrete type IV collagen and laminin for basement membrane
- Synthesize clotting molecules
- von Willebrand factor
- Secrete vasoactive factors that control blood flow
- Endothelin - vasoconstriction
- Nitric oxide - vasodilation
- Produce growth factors
- Fibroblasts growth factor (FGF
- Platelet-derived growth factor (PDGF)
- Produce cell adhesion molecules that mediate acute inflammatory response
- Selectins
- Integrins
6
Q
Weibel-Palade Bodies
A
Rod-shaped membrane-bound organelles within endothelial cells used for storage.
E.g. von Willebrand factor, P-selectins.
Derived from Golgi.
7
Q
Pericytes
A
- Undifferentiated mesenchymal cells which surrounds capillaries and post-capillary venules.
- Differentiates into endothelial cells, smooth muscle, or fibroblasts.
- May be contractile.
- Branched cytoplasmic processes wrap around vessels.
8
Q
Arteries
A
- High pressure vessels transporting blood away from heart
- Tunica media is dominant layer
- Narrow lumen with thicker wall
- Two basic types of arteries:
- Elastic arteries
- Aorta & pulmonary trunk
- Helps convert pulsatile blood flow to steadier flow via elastic recoil
- Muscular arteries
- Distributing arteries
- Includes most of the named arteries of the body
- Distribute blood to specific organs as needed
- Elastic arteries
9
Q
Arterioles
A
- Regulate blood pressure
- Regulate blood distribution to various organs & capillary beds
- Less than 5 layers of smooth muscle
- Metarterioles
- smallest arterioles
- discontinuous layer of smooth muscle
10
Q
Capillaries
A
- Location of metabolic exchange
- Can be smaller than diameter of RBC
- Consist of a single layer of endothelium and a basal lamina
- Discontinuous layer of pericytes may be present
11
Q
Venules
A
- Smallest vessels of venous system
- Two types of venules:
- Post-capillary venules
- Receive blood from capillaries
- Major site of WBC egress into extravascular tissues
- Muscular venules
- Contains at least one complete layer of smooth muscle
- Post-capillary venules
12
Q
Elastic Artery Structure
A
Aorta, pulmonary artery, etc.
- Tunica intima
- Endothelium
- Subendothelial connective tissue
- Internal elastic lamina
- Tunica media
- Layers of smooth muscle cells alternating with and attached to 40-60 fenestrated elastic laminae
- Vessels expand with systole and recoil with diastole
- Elasticity decreases with age
- Reticular fibers and ground substance
- No distinct external elastic lamina
- Layers of smooth muscle cells alternating with and attached to 40-60 fenestrated elastic laminae
- Tunica Adventitia
- Loose network of collagen and elastic fibers
- Fibroblasts and macrophages predominant
- Contain vasa vasorum
- poorly defined outer boundary
13
Q
Muscular Artery Structure
A
- Tunica Intima
- Endothelium
- Thinner subendothelial layer
- Prominent internal elastic lamina
- Appears scalloped if smooth muscle of media contracted
- Tunica Media
- Up to 40 layers of circularly arranged smooth muscle cells
- Few elastic fibers
- External elastric lamina often fragmented into several thin layers that extend into adventitia
- Tunica Adventitia
- Collagen and adipose
- Larger vessels have vasa vasorum
- Blends in with surrounding CT
14
Q
Arteriole Structure
A
- Endothelium
- +/- internal elastic lamina
- Tunica media only a few layers thick (call it less than 5)
- External elastic lamina typically absent
- Contains pre-capillary sphincters
15
Q
Metarterioles
A
- Smallest arterioles
- Discontinuous layers of smooth muscle
- Form preferential channels through capillary beds
- Arise from ordinary capillaries and drain into venules
- Contains precapillary sphincters
16
Q
Arteriosclerosis
A
Any thickening and hardening of arterial walls.
Atherosclerosis most common form:
- Hardening of arterial wall caused by fatty plaque (atheroma)
- Foam cells accumulate
- Smooth muscle cells proliferate in intima and produce ECM components contributing to fibrosis
- Weakens vessel & reduces luminal diameter
- Platelet aggregation & thrombus formation can cause sudden blockage
17
Q
Classes of Capillaries
A
Continuous
- found in most tissues
- tight junctions between endothelial cells
- no fenestrations
- pinocytotic vesicles transport substances across endothelium
Fenestrated
- Found in GI tract, kidney, endocrine organs
- Fenestrations or pores occur in thin areas of cytoplasm
- Have diaphragms in most organs
- Glomerular capillaries lack diaphragms
- More permeable than continuous
Sinusoidal
- Found in liver, bone marrow, spleen, adrenal cortex
- Leakiest capillary
- Wider diameter
- Irregular shape
- Large gaps between endothelial cells
- Basal lamina discontinuous or absent
18
Q
Venous Circulation
A
- Low pressure vessels returning blood to heart
- Larger lumens with thinner walls
- Valves prevent backflow
- Formed by a fold of the tunica intima
- Most common in large veins below level of heart
19
Q
Postcapillary Venules (PCVs)
Structure
A
- Consists mainly of endothelium, basal lamina, and discontinuous pericytes
- Reabsorb filtrate which leaked from capillaries
- Major site for vasoactive mediators
- Ex. Histamine and serotonin
- Main site of leukocyte diapedesis
- Via selectins, integrins, and ligands
20
Q
Diapedesis
A
- Lymphocytes leave PCV’s of lymph nodes
- Requires L-selectins on lymphocyte to bind ligand on endothelial surface
- In inflammation, all types of leukocytes leave PCVs at site
- Requires P-selectins and E-selectins on endothelial surface to bind ligands on leukocytes
- Expression of selectins induced by products of inflammatory process
- Binding causes cell to slow and roll
- Integrins then strengthen binding and cause cell to stop
- Leukocyte inserts pseudopod into endothelial intercellular junction
- Widened by histamine and leukotrienes from mast cells and basophils
21
Q
Muscular Venules
A
- Receives blood from postcapillary venules
- Differ from PCV in that they have true tunica media with 1-2 complete layers of smooth muscle
- Have thin tunica adventitia
22
Q
Medium & Large Vein
Structure
A
In artery-vein companion pairs, vein usually larger diameter and appears collapsed/irregular in shape.
- Tunica Intima
- Endothelium
- Thin subendothelial CT layer
- Occasional internal elastric lamina
- valves present in veins with >2mm diameter
- paired folds of intima
- Tunica Media
- Much thinner smooth muscle layer
- Tunica Adventitia
- Typically thickest layer of vessel wall
- Collagen and elastic fibers
- Fibroblasts
- Large veins like IVC may also contain bundles of longitudinally arranged smooth muscle
23
Q
Lymphatic Vessels
Characteristics
A
- Low pressure
- More permeable than capillaries
- Picks up excess interstitial fluid and returns it to circulation
- Found in most tissues except nervous system and bone marrow
- Major metastatic pathway
24
Q
Lymphatic Capillaries
A
- Begin as open ended endothelial tubes located near capillary beds
- Single layer of thin endothelial cells
- Basal lamina discontinuous or missing
- Often have valves
- Achoring filaments connect basal lamina to perivascular CT
- Prevents collapse
- Irregularly shaped
- May contain many lymphocytes
25
Lacteals
Specialized lymphatic capillaries located in the intestinal villi.
Absorbs dietary lipids in the form of chylomicrons.
26
Large Lymphatic Vessels
* Similar in structure to small veins
* Larger lumen
* Thinner walls
* Have valves
* **Right lymphatic duct** and **thoracic duct** return lymph to blood
* Have 3 tunics similar to large veins
27
Interstitial Pressure
Movement of fluid between capillaries and interstitium controlled by fluid forces:
1. **Osmotic Pressure**
* Created by concentration of albumin and other plasma proteins
* Draws fluid into venules from interstitium
2. **Hydrostatic Pressure**
1. Created by blood flow against capillary walls
2. Forces fluid out of capillaries into the interstitium
Arterial side: hydrostatic \> osmotic = fluid leaves vessels
Venous side: osmotic \> hydrostatic = fluid returns
Excess interstitial fluid causes _edema_
28
Causes of Edema
1. Increased venous hydrostatic pressure
* Left heart failure → pulmonary edema
* Right heart failure → peripheral edema
* Pregnant uterus compressing common iliac veins
2. Lymphatic obstruction preventing return
* Axillary lymph node remvoal
* Radiation damage
* Parasitic infection of lymphatic vessels (elephantiasis)
3. Capillary damage or increased permeability causing excessive leakage
* Burns
* Acute inflammation
* Histamine increases post capillary venule permeability
4. Decreased blood osmotic pressure causing decreased reabsorption
* Hepatic cirrhosis
* Nephritic syndrome
* Kidneys loss excessive proteins
* Malnutrition
29
Heart Chambers
* **Right atria**
* Receives blood from superior & inferior vena cava
* **Right ventricle**
* Pumps blood to pulmonary circulation
* **Left atria**
* Receives blood from pulmonary veins
* **Left ventricle**
* Pumps blood via aorta to systemic circulation
30
Endocardium
Continuous with tunica intima of blood vessels.
* Endothelium
* Subendothelial connective tissue
* Elastic fibers
* Collagen fibers
* No adipose
* More complex in ventricles where there is:
* Middle layer of CT and few smooth muscle cells
* **Subendocardial** layer of collagen and elastic fibers
* Contains Purkinje fibers
31
Myocardium
Continuous with tunica media of blood vessels.
* Consists mainly of cardiac muscle
* Involuntary striated muscle
* Ventricular myocytes slightly larger than atrial myocytes
* Myocardium much thicker in ventricles and on left side
* Dense capillary beds
32
Epicardium
Continuous with tunica adventitia of blood vessels.
* outermost layer is **visceral pericardium**
* _mesothelium_ plus _fibrous connective tissue_
* **subserosal connective tissue**
* abundant adipocytes
* contains large vessels of coronary circulation
* contains large nerve bundles from ANS
33
Cardiac Conduction System
Composed of modified cardiac myocytes
Rate modified by ANS
* **Sinoatrial (SA) node**
* Pacemaker
* Located deep in epicardium of right atrium
* **Atrioventricular (AV) node**
* Receives impulse from SA node
* Located in the interatrial septu near tricuspid valve
* Atrioventricular bundle (**bundle of His**)
* Continuous with AV node
* Only direct connection between atrial & ventricular myocardium
* Extends into interventricular septum
* Branches into **right** and **left bundle branches**
* Bundle branches end in **Purkinje fibers**
34
Cardiac Innervation
* Innervated by ANS
* Nerves end near SA node, AV node, and coronary arteries
* Parasympathetic → ACH → decreases HR & force of contractions, constricts coronary arteries
* Sympathetic → NorEpi → Increases HR & force of contraction, dilates coronary arteries
35
Nodal Cells
* Smaller in diameter than regular myocytes
* Paler due to fewer myofilaments
* Seperated by more CT
* Less interconnected
* Some gap junctions
* No intercalated disks
36
Purkinje Fibers
* Larger than ordinary cardiac myocytes
* Pale due to large amounts of glycogen
* Few myofilaments located at periphery of cell
* No T-tubles
* Irregular Z-lines
* Located in the layer of endocardium called **subendocardium**
* Ends first on papillary muscles
* causes them to contract before remainder of ventricle
* this "sets" AV valve leaflets preventing eversion back into atria during ventricular contraction
* Continues to rest of ventricular myocardium
37
Atrioventricular (AV) Valves
**Tricuspid valve** seperates right atrium from right ventricle.
**Bicuspid (mitral) valve** seperates left atrium from left ventricle.
* _Leaflets_ (cusps) are folds of endocardium covering fibrous core.
* Base of each leaflet anchored to an _annulus fibrosus_ of _cardiac skeleton_.
* Free edges of leaflets anchored to _papillary muscles_ by many _chordae tendinae_
* Chordae tendinae have CT cores covered by endocardium
38
Semilunar Valves
**Pulmonic valve** seperates right ventricle from pulmonary trunk.
**Atrial valve** seperates left ventricle from aorta.
* Consists of 3 pocket-shaped cusps
* Not associated with chordae tendinae or papillary muscles
39
Cardiac Skeleton
* Composed of dense collagenous tissue
* Not cartilage or bone
* Serves as anchoring point for myocytes
* Seperates ordinary atrial and ventricular myocytes from one another
* Heart valves are continuous with the skeleton
Has 3 main components:
1. **Four annuli fibrosi**
* Lies in the plane between atria and ventricles
* Surrounds the openings of the aorta, pulmonary artery, and atrioventricular orifices
* Provides attachment sites for leaflets of heart valves
2. **Two fibrous trigones** (right and left)
* Join the annuli fibrosi together
* AV bundle pierces right fibrous trigone to reach interventricular septum
3. **Septum membranaceum**
1. Extends downward from right fibrous trigone
2. Is the upper non-muscular part of interventricular septum
IMS: Microanatomy
flashcards
Decks in class (16)
# Cards
-
Integument35
-
Hypothalamus and pituitary43
-
Thyroid and Parathyroid22
-
Adrenal Glands21
-
Cartilage and Bone41
-
Bone Formation and Joints36
-
Blood87
-
Hematopoiesis42
-
Cardiovascular System39
-
Lymphoid Organs48
-
Respiratory System25
-
Oral Cavity and GI Track56
-
Liver, Gallbladder, Pancreas32
-
Urinary System35
-
Testis and Male Reproductive Tract52
-
Female Reproductive84
