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Flashcards in Histology/Embyology Deck (43):

Where is the majority of your blood at one time?

65% is in the peripheral veins


What are the 3 layers of blood vessels?

•Inner layer: Tunica intima
• Middle layer: Tunica media
• Outer layer: Tunica adventitia


Tunica intima

Made up of a single layer of squamous epithelial cells termed endothelial cells (collectively the endothelium) supported by a basal lamina and a thin layer of connective tissue.


Tunica media

Tunica media made up predominately of muscle (in some areas there is a significant amount of elastic tissue). This layer varies tremendously and in some cases virtually disappears.


Tunica adventitia

Tunica adventitia made up of supporting connective tissue.


Elastic arteries

Largest arteries e.g. aorta. Contain many sheets of elastic fibres in their tunica media to provide elastic recoil


What are the unique histology features of arterioles?

Arterioles have only one or two layers of smooth muscle in their tunica media and almost no adventitia. Typical diameter: 30-200µm.


What are the unique histology features of capillaries?

Essentially composed of endothelial cells and a basal lamina. They often have pericytes (P) at intervals just outside the basal lamina. These are connective tissue cells that have contractile properties. Typical diameter: 4-8µm


What are the 3 types of capillaries?

1) Continuous (muscle, connective tissue, lung, skin, nerve)
2) Fenestrated (mucosa of the gut, endocrine glands, glomeruli of the kidney)
3) Sinusoidal or discontinuous (liver, spleen and bone marrow)


What are the unique histology features of post capillary venules?

Endothelial cells associated with pericytes or occasional smooth muscle cells. 10-30µm diameter


What are the unique histology features of veins?

Relatively thin tunica media relative to the size of the lumen. Very thin smooth muscle layer as the pressure is far lower. Typically have valves in them which are essentially invaginations of the tunica intima


What are the 2 main types of arteries?

Muscular and elastic


From superficial to deep, what are the 3 layers of the heart?

Epicardium, myocardium and endocardium



Loose connective tissue containing small blood vessels and nerves and the branches of the impulse conducting system. Only found in certain areas of the heart.


In which layer of the heart do the coronary vessels lie?

In the fat surface of the epicardium


What are the 2 layers of the pericardium?

1) Fibrous pericardium (sac of tough fibrocollagenous connective tissue).
2) Serous pericardium (layer of simple squamous epithelium (termed mesothelium), backed by a basal lamina and connective tissue. 2 sublayers: parietal and visceral pericardium)


Fibrous skeleton

Fibrous ‘skeleton’ formed by thick bands of fibrous connective tissue around the heart valves, between the atria, and between the ventricles. This connective tissue supports the valves, but also provides the attachment for the cardiac muscle fibres. It also acts as electrical insulation between the atria and ventricles


What are the 3 types of cardiac muscle cells?

• Contractile cells (99%)
• Pacemaker cells
• Conducting cells


In which 2 types of vessels does lymph travel?

Venous vessels and lymphatic vessels


What helps produce flow in the lymphatic vessels?

No central pump, but smooth muscle in walls, hydrostatic pressure in the tissue and compression of the vessels by voluntary muscle, combined with valves in the vessels, produces flow.


**What are the main differences between foetal and adult circulation?

- The placenta is included in the circulation
- The lungs are fluid filled and unexpanded
- The liver has little role in nutrition and waste management
- The gut is not in use – only for swallowing amniotic fluid and secreting bile etc


What are the main functions of the placenta?

- Fetal homeostasis
- Gas exchange
- Acid base balance
- Nutrient transport to fetes
- Waste product transport from fetes
- Hormone production
• Proastaglandin 2
- Transport of IgG


Which arteries supply the placenta and which veins drain it?

Umbilical arteries and umbilical vein


What are the 3 foetal shunts present in the feta circulation?

1) Ductus Venosus
2) Foramen Ovale
3) Ductus Arteriosus


True or False: The LV is dominant in the foetus

False, the RV is dominant


Ductus venosus

Connects the umbilical vein to the inferior vena cava, bypassing the liver


Formane ovale

Opening in atrial septum connecting RA to LA - allows the majority of blood go to the head where it is needed most


Ductus arteriosus

Connects pulmonary bifurcation to the descending aorta


Why is it important that the RV is dominant in foetal circulation?

Foramen ovale is membrane flap on left atrium side so higher pressure on the right side forces blood to flow from the right side to the left. So when the baby is born and the pressure rises on the left side, this closes the membrane flap over.


Which hormone is involved in keeping the ductus arteriosus open?

Prostaglandin 2 (PGE2)


Why shouldn't you have ibuprofen when pregnant?

Inhibits prostaglandin so could cause the ductus to close over and this is fatal for the baby


What are the main changes in foetal circulation following birth?

- Baby inflates lungs with a massive breath and cries - This creates pressure to inflate the alveoli and increase sats fro 60%
- Cord clamped and cut - Abruptly removing the placenta from the circulation and causing the systemic vascular resistance to rise
- Ductus arteriosus closure


What does the ductus arteriosus become after closure?

Ligamentum arteriosum


What causes the ductus arteriousus to close?

1. Fall in pulmonary vascular resistance reduces blood flow through the duct
2. Rising oxygen tension has a direct effect on the duct smooth muscle causing constriction
3. The loss of circulating PGE2 from the placenta and increased PGE2 metabolism in lung


What is the common cause for a patent ductus arteriosus in newborns?

Underdevelopment of the lungs so not able to create the pressure needed


What is the treatment for a patent ductus arteriosus?

Monitoring, NSAIDs and surgery


Duct dependent circulation

Some congenital heart disease causes a “duct dependent circulation” such as interruption of the aortic arch. This is fine in utero but once born, the baby is completely dependent on the ductus arteriosus so if this closes then the baby rapidly dies


What is the treatment of a duct dependent circulation?

IV prostaglandin E2 can be used to keep the duct open until an alternative shunt established or definitive surgery carried out


Persistent pulmonary hypertension

Pressure in the lungs fails to drop when the baby is born, also means shunts remain patent e.g. PFO and PDA


Which germ layer is the heart from?

Visceral mesoderm


What are the 5 swellings/dilations of the heart tube?

1) Sinus census
2) Atrium
3) Ventricle
4) Bulbus cordis
5) Truncus arteriosus (developing aorta and pulmonary trunk)


Which cells line the developing heart tube?

Cardio myocytes, which beat synchronously and ensures unidirectional blood flow


Which two septa divide and form the 2 atria?

Septum premum and septum secundum