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Capillaries Facts & Worksheets

Capillaries are little blood vessels that run throughout your body that facilitate the connection of arteries and veins

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Capillaries are little blood vessels that run throughout your body. They facilitate the connection of arteries and veins and the exchange of specific components between blood and tissues. Because of this, capillaries are numerous in highly active tissues such as your muscles, liver, and kidneys.

See the fact file below for more information on Capillaries, or you can download our 31-page Capillaries worksheet pack to utilize within the classroom or home environment.

Key Facts & Information

STRUCTURE AND FUNCTION

  • Most capillaries can be 8 to 10 micrometers ( 1 micrometer is 0.001 mm) in diameter. Because of these, red blood cells pass through in a single file line because capillaries are very tiny.
  • The two cell layers seen in capillaries are endothelial cells and epithelial layers. The endothelial cells are inside the capillary, which helps regulate the movement of gases, nutrients, and liquids. At the same time, the epithelial layers encircle the endothelial cells for protection.
  • A thin cell layer called the endothelium, surrounded by an even thinner layer known as a basement membrane, makes up the capillaries.
  • Capillaries are a little “leakier” than other blood vessels due to their single-layer endothelium composition, which varies among the different types of capillaries and the surrounding basement membrane. This makes it easier for molecules like oxygen and other substances to enter your body’s cells.
  • Additionally, capillaries are used by the white blood cells of your immune system to reach infected or otherwise inflammatory-damaged areas.

Capillaries can perform a variety of tasks due to their three different structures:

  • Continuous Nonfenestrated Capillaries – Only tiny molecules can pass through the lining of continuous nonfenestrated capillaries. Along with fat and muscular tissue, the nervous system also has capillaries of this sort. The brain’s continuous capillaries are an exception, though.
  • These capillaries are a component of the blood-brain barrier, which safeguards your brain by limiting the nutrients that can pass.
  • These capillary types are the most prevalent. Things, including air, water, sugar (glucose), and certain hormones, can travel through the tiny spaces between their endothelial cells.
  • Since there are no gaps between the endothelial cells in the continuous capillaries in this region, their surrounding basement membrane is likewise thicker.
  • Fenestrated Capillaries – Fenestrated capillaries allow a lot of material exchange, for example, the kidneys, small intestines, and endocrine glands contain this capillary type.
  • Compared to continuous nonfenestrated capillaries, fenestrated capillaries are “leakier.” In addition to tiny cell-to-cell spaces, they have small pores in their walls that permit the exchange of larger molecules.
  • These capillaries are in tissues and organs that need frequent blood exchanges—areas like the small intestine, where nutrients from food are absorbed, and the kidneys, where blood’s waste materials are filtered.
  • Sinusoidal Capillaries – These capillaries are the most uncommon and “leakiest” kind. In sinusoid capillaries, it can exchange large molecules and even cells. It can also allow some chemicals to pass through. They may do this because their capillary wall has numerous more significant gaps in addition to pores and smaller apertures. Additionally, the adjacent basement membrane has multiple openings and is not complete.
  • These capillaries can be in the liver, spleen, bone marrow, and other tissues. It enables freshly made red blood cells to reach the bloodstream and start circulating in your bone marrow.
  • Capillaries link your venous system to your arterial system, which contains the blood arteries that carry blood away from your heart. The blood arteries that return blood to your heart are a part of your venous system. 
  • Your organs receive oxygen-rich blood from the heart through arteries. The body uses veins to eliminate waste and low-oxygen blood.
  • Passive Diffusion – This occurs when material moves from a region with a higher concentration to one with a lower concentration.
  • Pinocytosis – This refers to the process through which your body’s cells actively take in tiny molecules, such as lipids and proteins.

CAPILLARIES AND OTHER ORGANS

Various organs and systems are supported by capillaries as well. It helps to keep multiple organs and systems by doing the following:

  • Bone Marrow – Allows new blood cells to enter your bloodstream.
  • Brain – The brain forms the blood-brain barrier. This structure protects against the passage of contaminants while supplying nutrients to the brain.
  • Lymphatic System – Transfers fluid from tissues to lymph nodes.
  • Endocrine system – Sends hormones to particular organs.
  • Kidneys – The kidneys’ peritubular capillaries generate urine, absorb water and sodium, and filter blood.
  • Liver – Eliminates germs and damaged red blood cells.
  • Lungs – Exhales carbon dioxide and absorb oxygen.

CONDITIONS AND DISORDERS

  • Even though capillaries are relatively tiny, anything that disrupts their regular operation might result in apparent symptoms or potentially dangerous medical issues. 
  • Capillaries may break frequently. They may accompany violent vomiting or coughing. Your skin develops little red spots, which often go away by themselves.

Injuries to capillaries can also result from:

  • Arteriovenous malformation (AVM) – A series of tangled arteries and veins that may bypass the capillaries in the brain or spinal cord. Your brain and spinal cord aren’t the only places where AV abnormalities can occur. They can also affect the organs, the trunk, or the limbs.
  • AVM is typically not symptomatic. Hence it is typically first identified while trying to determine another condition. But occasionally, it can lead to headaches, pain, weakness, difficulties with mobility, speech, or vision, and seizures.
  • AVM is an uncommon disorder that frequently exists at birth. Surgery can remove or close the AVM lesion. Patients diagnosed can manage symptoms like pain or headaches with medication.
  • Capillary Angiosarcoma – A condition of endothelial cell cancer that can impact the capillaries.
  • Capillary Leak Syndrome – A disorder that produces a sudden drop in blood pressure. Sometimes it calls for emergency care.
  • These attacks typically come with a few early warning indicators, such as nasal obstruction, cough, nausea, headache, abdomen, ache, lightheadedness, fainting, and swollen legs and arms.
  • Hereditary Hemorrhagic Telangiectasia – A genetic blood vessel illness that results in abnormal growths (telangiectases) that have the potential to explode. Another name for it is Osler-Weber-Rendu syndrome.
  • Macular degeneration – Inner-eye damage brought about by capillary leakage.
  • Microcephaly-Capillary Malformation Syndrome– Wide capillaries are a sign of microcephaly-capillary malformation syndrome, which affects people whose skulls are relatively small.
  • Spider Nevus – A small blood vessel growth commonly appears on the face, neck, or chest. It is additionally known as spider telangiectasia or spider angioma.
  • Strawberry Birthmark – A cluster of bright red blood vessels on the skin’s surface.
  • Vasculitis – An inflammation of the blood vessels that may impact the capillaries. It may result in issues like obstructions and rupture.
  • Port Wine Stains – Birthmarks like port wine stains are brought on by enlarging the skin’s capillaries. The illness gets its name from the spreading, which makes the skin seem pink or dark red. They may thicken and darken in color over time.
  • Port wine stains don’t disappear independently but don’t spread to other places. Most of the time, port wine stains don’t need treating, though laser therapy may assist in making them lighter in color.
  • Petechiae – Petechiae are little, rounded skin spots. They can be red or purple and are usually around the size of a pinhead with dull skin. They develop when blood leaks from capillaries into the skin. When you press on them, they don’t become lighter in hue.
  • Petechiae are often a sign of one or more of the following conditions: infectious illnesses, including Rocky Mountain, spotted fever, meningococcal disease, scarlet fever, strain injury from vomiting or coughing, leukemia, scurvy, and low amounts of platelets.
  • Penicillin is one drug that can also result in petechiae as a side effect.

HOW TO KEEP CAPILLARIES HEALTHY

You may take good care of your capillaries by improving your vascular health.

This includes:

  • Having an active way of life.
  • Limiting the usage of alcohol and caffeine.
  • Keeping a healthy weight.
  • If you use tobacco, you should stop smoking.

Capillaries Worksheets

This fantastic bundle includes everything you need to know about Capillaries across 31 in-depth pages. These ready-to-use worksheets are perfect for teaching kids about Capillaries, little blood vessels that run throughout your body.

Download includes the following worksheets

  • Capillaries Facts
  • Artery or Vein?
  • Exchange
  • Condition and Disorders
  • Transport Vessels
  • Capillary types
  • Organs and Systems
  • Science in Everyday Life
  • Arterial and Venous System
  • Blood Type
  • Poster Making

Frequently Asked Questions

What are capillaries?

Capillaries are tiny blood vessels that connect arteries to veins and play a crucial role in exchanging oxygen, nutrients, and waste products between the bloodstream and tissues.

What is the structure of capillaries?

Capillaries comprise a single layer of endothelial cells surrounded by basement membrane and smooth muscle cells. Their small diameter (typically 5-10 microns) allows for the exchange of substances between the blood and tissues.

What is the role of capillaries in the circulatory system?

Capillaries are the site of exchange between the bloodstream and tissues. Oxygen, nutrients, and hormones diffuse from the bloodstream into the tissues, while carbon dioxide and waste products diffuse from the tissues into the bloodstream.

What happens in the capillaries during diseases?

In some diseases, such as inflammation or cancer, the capillaries may become leaky, allowing fluid and proteins to escape into the surrounding tissues. This can lead to edema (swelling) and tissue damage. In other diseases, such as cardiovascular disease, capillaries may narrow or block blood flow and oxygen supply to the tissues.

Can capillaries be regenerated or repaired?

Yes, capillaries can be regenerated and repaired through angiogenesis, in which new blood vessels are formed from existing ones. This process can occur in response to signals from growth factors and cytokines and can be crucial in tissue repair and wound healing. In some diseases, such as cancer, abnormal angiogenesis can occur, forming new blood vessels that support tumor growth.

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Use With Any Curriculum

These worksheets have been specifically designed for use with any international curriculum. You can use these worksheets as-is, or edit them using Google Slides to make them more specific to your own student ability levels and curriculum standards.

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