Histology/Embyology

Question 1

Where is the majority of your blood at one time?

Answer 1

65% is in the peripheral veins

Question 2

What are the 3 layers of blood vessels?

Answer 2

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

Question 3

Tunica intima

Answer 3

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.

Question 4

Tunica media

Answer 4

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.

Question 5

Tunica adventitia

Answer 5

Tunica adventitia made up of supporting connective tissue.

Question 6

Elastic arteries

Answer 6

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

Question 7

What are the unique histology features of arterioles?

Answer 7

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

Question 8

What are the unique histology features of capillaries?

Answer 8

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

Question 9

What are the 3 types of capillaries?

Answer 9

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)

Question 10

What are the unique histology features of post capillary venules?

Answer 10

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

Question 11

What are the unique histology features of veins?

Answer 11

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

Question 12

What are the 2 main types of arteries?

Answer 12

Muscular and elastic

Question 13

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

Answer 13

Epicardium, myocardium and endocardium

Question 14

Subendocardium

Answer 14

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.

Question 15

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

Answer 15

In the fat surface of the epicardium

Question 16

What are the 2 layers of the pericardium?

Answer 16

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)

Question 17

Fibrous skeleton

Answer 17

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

Question 18

What are the 3 types of cardiac muscle cells?

Answer 18

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

Question 19

In which 2 types of vessels does lymph travel?

Answer 19

Venous vessels and lymphatic vessels

Question 20

What helps produce flow in the lymphatic vessels?

Answer 20

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.

Question 21

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

Answer 21

• 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

Question 22

What are the main functions of the placenta?

Answer 22

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

Question 23

Which arteries supply the placenta and which veins drain it?

Answer 23

Umbilical arteries and umbilical vein

Question 24

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

Answer 24

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

Question 25

True or False: The LV is dominant in the foetus

Answer 25

False, the RV is dominant

Question 26

Ductus venosus

Answer 26

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

Question 27

Formane ovale

Answer 27

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

Question 28

Ductus arteriosus

Answer 28

Connects pulmonary bifurcation to the descending aorta

Question 29

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

Answer 29

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.

Question 30

Which hormone is involved in keeping the ductus arteriosus open?

Answer 30

Prostaglandin 2 (PGE2)

Question 31

Why shouldn't you have ibuprofen when pregnant?

Answer 31

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

Question 32

What are the main changes in foetal circulation following birth?

Answer 32

- 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

Question 33

What does the ductus arteriosus become after closure?

Answer 33

Ligamentum arteriosum

Question 34

What causes the ductus arteriousus to close?

Answer 34

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

Question 35

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

Answer 35

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

Question 36

What is the treatment for a patent ductus arteriosus?

Answer 36

Monitoring, NSAIDs and surgery

Question 37

Duct dependent circulation

Answer 37

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

Question 38

What is the treatment of a duct dependent circulation?

Answer 38

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

Question 39

Persistent pulmonary hypertension

Answer 39

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

Question 40

Which germ layer is the heart from?

Answer 40

Visceral mesoderm

Question 41

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

Answer 41

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

Question 42

Which cells line the developing heart tube?

Answer 42

Cardio myocytes, which beat synchronously and ensures unidirectional blood flow

Question 43

Which two septa divide and form the 2 atria?

Answer 43

Septum premum and septum secundum